EDIT

/**

 * jQuery Form Plugin

 * version: 2.12 (06/07/2008)

 * @requires jQuery v1.2.2 or later

 *

 * Examples and documentation at: http://malsup.com/jquery/form/

 * Dual licensed under the MIT and GPL licenses:

 *   http://www.opensource.org/licenses/mit-license.php

 *   http://www.gnu.org/licenses/gpl.html

 */

(function($) {

/*

    Usage Note:  

    -----------

    Do not use both ajaxSubmit and ajaxForm on the same form.  These

    functions are intended to be exclusive.  Use ajaxSubmit if you want

    to bind your own submit handler to the form.  For example,

    $(document).ready(function() {

        $('#myForm').bind('submit', function() {

            $(this).ajaxSubmit({

                target: '#output'

            });

            return false; // <-- important!

        });

    });

    Use ajaxForm when you want the plugin to manage all the event binding

    for you.  For example,

    $(document).ready(function() {

        $('#myForm').ajaxForm({

            target: '#output'

        });

    });

    When using ajaxForm, the ajaxSubmit function will be invoked for you

    at the appropriate time.  

*/

/**

 * ajaxSubmit() provides a mechanism for immediately submitting 

 * an HTML form using AJAX.

 */

$.fn.ajaxSubmit = function(options) {

    // fast fail if nothing selected (http://dev.jquery.com/ticket/2752)

    if (!this.length) {

        log('ajaxSubmit: skipping submit process - no element selected');

        return this;

    }

    if (typeof options == 'function')

        options = { success: options };

    options = $.extend({

        url:  this.attr('action') || window.location.toString(),

        type: this.attr('method') || 'GET'

    }, options || {});

    // hook for manipulating the form data before it is extracted;

    // convenient for use with rich editors like tinyMCE or FCKEditor

    var veto = {};

    this.trigger('form-pre-serialize', [this, options, veto]);

    if (veto.veto) {

        log('ajaxSubmit: submit vetoed via form-pre-serialize trigger');

        return this;

   }

    var a = this.formToArray(options.semantic);

    if (options.data) {

        options.extraData = options.data;

        for (var n in options.data)

            a.push( { name: n, value: options.data[n] } );

    }

    // give pre-submit callback an opportunity to abort the submit

    if (options.beforeSubmit && options.beforeSubmit(a, this, options) === false) {

        log('ajaxSubmit: submit aborted via beforeSubmit callback');

        return this;

    }    

    // fire vetoable 'validate' event

    this.trigger('form-submit-validate', [a, this, options, veto]);

    if (veto.veto) {

        log('ajaxSubmit: submit vetoed via form-submit-validate trigger');

        return this;

    }    

    var q = $.param(a);

    if (options.type.toUpperCase() == 'GET') {

        options.url += (options.url.indexOf('?') >= 0 ? '&' : '?') + q;

        options.data = null;  // data is null for 'get'

    }

    else

        options.data = q; // data is the query string for 'post'

    var $form = this, callbacks = [];

    if (options.resetForm) callbacks.push(function() { $form.resetForm(); });

    if (options.clearForm) callbacks.push(function() { $form.clearForm(); });

    // perform a load on the target only if dataType is not provided

    if (!options.dataType && options.target) {

        var oldSuccess = options.success || function(){};

        callbacks.push(function(data) {

            $(options.target).html(data).each(oldSuccess, arguments);

        });

    }

    else if (options.success)

        callbacks.push(options.success);

    options.success = function(data, status) {

        for (var i=0, max=callbacks.length; i < max; i++)

            callbacks[i](data, status, $form);

    };

    // are there files to upload?

    var files = $('input:file', this).fieldValue();

    var found = false;

    for (var j=0; j < files.length; j++)

        if (files[j])

            found = true;

    // options.iframe allows user to force iframe mode

   if (options.iframe || found) { 

       // hack to fix Safari hang (thanks to Tim Molendijk for this)

       // see:  http://groups.google.com/group/jquery-dev/browse_thread/thread/36395b7ab510dd5d

       if ($.browser.safari && options.closeKeepAlive)

           $.get(options.closeKeepAlive, fileUpload);

       else

           fileUpload();

       }

   else

       $.ajax(options);

    // fire 'notify' event

    this.trigger('form-submit-notify', [this, options]);

    return this;

    // private function for handling file uploads (hat tip to YAHOO!)

    function fileUpload() {

        var form = $form[0];

        if ($(':input[@name=submit]', form).length) {

            alert(t('Error: Form elements must not be named "submit".'));

            return;

        }

        var opts = $.extend({}, $.ajaxSettings, options);

        var id = 'jqFormIO' + (new Date().getTime());

        var $io = $('<iframe id="' + id + '" name="' + id + '" />');

        var io = $io[0];

        if ($.browser.msie || $.browser.opera) 

            io.src = 'javascript:false;document.write("");';

        $io.css({ position: 'absolute', top: '-1000px', left: '-1000px' });

        var xhr = { // mock object

            responseText: null,

            responseXML: null,

            status: 0,

            statusText: 'n/a',

            getAllResponseHeaders: function() {},

            getResponseHeader: function() {},

            setRequestHeader: function() {}

        };

        var g = opts.global;

        // trigger ajax global events so that activity/block indicators work like normal

        if (g && !$.active++) $.event.trigger("ajaxStart");

        if (g) $.event.trigger("ajaxSend", [xhr, opts]);

        var cbInvoked = 0;

        var timedOut = 0;

        // add submitting element to data if we know it

        var sub = form.clk;

        if (sub) {

            var n = sub.name;

            if (n && !sub.disabled) {

                options.extraData = options.extraData || {};

                options.extraData[n] = sub.value;

                if (sub.type == "image") {

                    options.extraData[name+'.x'] = form.clk_x;

                    options.extraData[name+'.y'] = form.clk_y;

                }

            }

        }

        // take a breath so that pending repaints get some cpu time before the upload starts

        setTimeout(function() {

            // make sure form attrs are set

            var t = $form.attr('target'), a = $form.attr('action');

            $form.attr({

                target:   id,

                encoding: 'multipart/form-data',

                enctype:  'multipart/form-data',

                method:   'POST',

                action:   opts.url

            });

            // support timout

            if (opts.timeout)

                setTimeout(function() { timedOut = true; cb(); }, opts.timeout);

            // add "extra" data to form if provided in options

            var extraInputs = [];

            try {

                if (options.extraData)

                    for (var n in options.extraData)

                        extraInputs.push(

                            $('<input type="hidden" name="'+n+'" value="'+options.extraData[n]+'" />')

                                .appendTo(form)[0]);

                // add iframe to doc and submit the form

                $io.appendTo('body');

                io.attachEvent ? io.attachEvent('onload', cb) : io.addEventListener('load', cb, false);

                form.submit();

            }

            finally {

                // reset attrs and remove "extra" input elements

                $form.attr('action', a);

                t ? $form.attr('target', t) : $form.removeAttr('target');

                $(extraInputs).remove();

            }

        }, 10);

        function cb() {

            if (cbInvoked++) return;

            io.detachEvent ? io.detachEvent('onload', cb) : io.removeEventListener('load', cb, false);

            var operaHack = 0;

            var ok = true;

            try {

                if (timedOut) throw 'timeout';

                // extract the server response from the iframe

                var data, doc;

                doc = io.contentWindow ? io.contentWindow.document : io.contentDocument ? io.contentDocument : io.document;

                if (doc.body == null && !operaHack && $.browser.opera) {

                    // In Opera 9.2.x the iframe DOM is not always traversable when

                    // the onload callback fires so we give Opera 100ms to right itself

                    operaHack = 1;

                    cbInvoked--;

                    setTimeout(cb, 100);

                    return;

                }

                xhr.responseText = doc.body ? doc.body.innerHTML : null;

                xhr.responseXML = doc.XMLDocument ? doc.XMLDocument : doc;

                xhr.getResponseHeader = function(header){

                    var headers = {'content-type': opts.dataType};

                    return headers[header];

                };

                if (opts.dataType == 'json' || opts.dataType == 'script') {

                    var ta = doc.getElementsByTagName('textarea')[0];

                    xhr.responseText = ta ? ta.value : xhr.responseText;

                }

                else if (opts.dataType == 'xml' && !xhr.responseXML && xhr.responseText != null) {

                    xhr.responseXML = toXml(xhr.responseText);

                }

                data = $.httpData(xhr, opts.dataType);

            }

            catch(e){

                ok = false;

                $.handleError(opts, xhr, 'error', e);

            }

            // ordering of these callbacks/triggers is odd, but that's how $.ajax does it

            if (ok) {

                opts.success(data, 'success');

                if (g) $.event.trigger("ajaxSuccess", [xhr, opts]);

            }

            if (g) $.event.trigger("ajaxComplete", [xhr, opts]);

            if (g && ! --$.active) $.event.trigger("ajaxStop");

            if (opts.complete) opts.complete(xhr, ok ? 'success' : 'error');

            // clean up

            setTimeout(function() {

                $io.remove();

                xhr.responseXML = null;

            }, 100);

        };

        function toXml(s, doc) {

            if (window.ActiveXObject) {

                doc = new ActiveXObject('Microsoft.XMLDOM');

                doc.async = 'false';

                doc.loadXML(s);

            }

            else

                doc = (new DOMParser()).parseFromString(s, 'text/xml');

            return (doc && doc.documentElement && doc.documentElement.tagName != 'parsererror') ? doc : null;

        };

    };

};

/**

 * ajaxForm() provides a mechanism for fully automating form submission.

 *

 * The advantages of using this method instead of ajaxSubmit() are:

 *

 * 1: This method will include coordinates for <input type="image" /> elements (if the element

 *    is used to submit the form).

 * 2. This method will include the submit element's name/value data (for the element that was

 *    used to submit the form).

 * 3. This method binds the submit() method to the form for you.

 *

 * The options argument for ajaxForm works exactly as it does for ajaxSubmit.  ajaxForm merely

 * passes the options argument along after properly binding events for submit elements and

 * the form itself.

 */ 

$.fn.ajaxForm = function(options) {

    return this.ajaxFormUnbind().bind('submit.form-plugin',function() {

        $(this).ajaxSubmit(options);

        return false;

    }).each(function() {

        // store options in hash

        $(":submit,input:image", this).bind('click.form-plugin',function(e) {

            var $form = this.form;

            $form.clk = this;

            if (this.type == 'image') {

                if (e.offsetX != undefined) {

                    $form.clk_x = e.offsetX;

                    $form.clk_y = e.offsetY;

                } else if (typeof $.fn.offset == 'function') { // try to use dimensions plugin

                    var offset = $(this).offset();

                    $form.clk_x = e.pageX - offset.left;

                    $form.clk_y = e.pageY - offset.top;

                } else {

                    $form.clk_x = e.pageX - this.offsetLeft;

                    $form.clk_y = e.pageY - this.offsetTop;

                }

            }

            // clear form vars

            setTimeout(function() { $form.clk = $form.clk_x = $form.clk_y = null; }, 10);

        });

    });

};

// ajaxFormUnbind unbinds the event handlers that were bound by ajaxForm

$.fn.ajaxFormUnbind = function() {

    this.unbind('submit.form-plugin');

    return this.each(function() {

        $(":submit,input:image", this).unbind('click.form-plugin');

    });

};

/**

 * formToArray() gathers form element data into an array of objects that can

 * be passed to any of the following ajax functions: $.get, $.post, or load.

 * Each object in the array has both a 'name' and 'value' property.  An example of

 * an array for a simple login form might be:

 *

 * [ { name: 'username', value: 'jresig' }, { name: 'password', value: 'secret' } ]

 *

 * It is this array that is passed to pre-submit callback functions provided to the

 * ajaxSubmit() and ajaxForm() methods.

 */

$.fn.formToArray = function(semantic) {

    var a = [];

    if (this.length == 0) return a;

    var form = this[0];

    var els = semantic ? form.getElementsByTagName('*') : form.elements;

    if (!els) return a;

    for(var i=0, max=els.length; i < max; i++) {

        var el = els[i];

        var n = el.name;

        if (!n) continue;

        if (semantic && form.clk && el.type == "image") {

            // handle image inputs on the fly when semantic == true

            if(!el.disabled && form.clk == el)

                a.push({name: n+'.x', value: form.clk_x}, {name: n+'.y', value: form.clk_y});

            continue;

        }

        var v = $.fieldValue(el, true);

        if (v && v.constructor == Array) {

            for(var j=0, jmax=v.length; j < jmax; j++)

                a.push({name: n, value: v[j]});

        }

        else if (v !== null && typeof v != 'undefined')

            a.push({name: n, value: v});

    }

    if (!semantic && form.clk) {

        // input type=='image' are not found in elements array! handle them here

        var inputs = form.getElementsByTagName("input");

        for(var i=0, max=inputs.length; i < max; i++) {

            var input = inputs[i];

            var n = input.name;

            if(n && !input.disabled && input.type == "image" && form.clk == input)

                a.push({name: n+'.x', value: form.clk_x}, {name: n+'.y', value: form.clk_y});

        }

    }

    return a;

};

/**

 * Serializes form data into a 'submittable' string. This method will return a string

 * in the format: name1=value1&name2=value2

 */

$.fn.formSerialize = function(semantic) {

    //hand off to jQuery.param for proper encoding

    return $.param(this.formToArray(semantic));

};

/**

 * Serializes all field elements in the jQuery object into a query string.

 * This method will return a string in the format: name1=value1&name2=value2

 */

$.fn.fieldSerialize = function(successful) {

    var a = [];

    this.each(function() {

        var n = this.name;

        if (!n) return;

        var v = $.fieldValue(this, successful);

        if (v && v.constructor == Array) {

            for (var i=0,max=v.length; i < max; i++)

                a.push({name: n, value: v[i]});

        }

        else if (v !== null && typeof v != 'undefined')

            a.push({name: this.name, value: v});

    });

    //hand off to jQuery.param for proper encoding

    return $.param(a);

};

/**

 * Returns the value(s) of the element in the matched set.  For example, consider the following form:

 *

 *  <form><fieldset>

 *      <input name="A" type="text" />

 *      <input name="A" type="text" />

 *      <input name="B" type="checkbox" value="B1" />

 *      <input name="B" type="checkbox" value="B2"/>

 *      <input name="C" type="radio" value="C1" />

 *      <input name="C" type="radio" value="C2" />

 *  </fieldset></form>

 *

 *  var v = $(':text').fieldValue();

 *  // if no values are entered into the text inputs

 *  v == ['','']

 *  // if values entered into the text inputs are 'foo' and 'bar'

 *  v == ['foo','bar']

 *

 *  var v = $(':checkbox').fieldValue();

 *  // if neither checkbox is checked

 *  v === undefined

 *  // if both checkboxes are checked

 *  v == ['B1', 'B2']

 *

 *  var v = $(':radio').fieldValue();

 *  // if neither radio is checked

 *  v === undefined

 *  // if first radio is checked

 *  v == ['C1']

 *

 * The successful argument controls whether or not the field element must be 'successful'

 * (per http://www.w3.org/TR/html4/interact/forms.html#successful-controls).

 * The default value of the successful argument is true.  If this value is false the value(s)

 * for each element is returned.

 *

 * Note: This method *always* returns an array.  If no valid value can be determined the

 *       array will be empty, otherwise it will contain one or more values.

 */

$.fn.fieldValue = function(successful) {

    for (var val=[], i=0, max=this.length; i < max; i++) {

        var el = this[i];

        var v = $.fieldValue(el, successful);

        if (v === null || typeof v == 'undefined' || (v.constructor == Array && !v.length))

            continue;

        v.constructor == Array ? $.merge(val, v) : val.push(v);

    }

    return val;

};

/**

 * Returns the value of the field element.

 */

$.fieldValue = function(el, successful) {

    var n = el.name, t = el.type, tag = el.tagName.toLowerCase();

    if (typeof successful == 'undefined') successful = true;

    if (successful && (!n || el.disabled || t == 'reset' || t == 'button' ||

        (t == 'checkbox' || t == 'radio') && !el.checked ||

        (t == 'submit' || t == 'image') && el.form && el.form.clk != el ||

        tag == 'select' && el.selectedIndex == -1))

            return null;

    if (tag == 'select') {

        var index = el.selectedIndex;

        if (index < 0) return null;

        var a = [], ops = el.options;

        var one = (t == 'select-one');

        var max = (one ? index+1 : ops.length);

        for(var i=(one ? index : 0); i < max; i++) {

            var op = ops[i];

            if (op.selected) {

                // extra pain for IE...

                var v = $.browser.msie && !(op.attributes['value'].specified) ? op.text : op.value;

                if (one) return v;

                a.push(v);

            }

        }

        return a;

    }

    return el.value;

};

/**

 * Clears the form data.  Takes the following actions on the form's input fields:

 *  - input text fields will have their 'value' property set to the empty string

 *  - select elements will have their 'selectedIndex' property set to -1

 *  - checkbox and radio inputs will have their 'checked' property set to false

 *  - inputs of type submit, button, reset, and hidden will *not* be effected

 *  - button elements will *not* be effected

 */

$.fn.clearForm = function() {

    return this.each(function() {

        $('input,select,textarea', this).clearFields();

    });

};

/**

 * Clears the selected form elements.

 */

$.fn.clearFields = $.fn.clearInputs = function() {

    return this.each(function() {

        var t = this.type, tag = this.tagName.toLowerCase();

        if (t == 'text' || t == 'password' || tag == 'textarea')

            this.value = '';

        else if (t == 'checkbox' || t == 'radio')

            this.checked = false;

        else if (tag == 'select')

            this.selectedIndex = -1;

    });

};

/**

 * Resets the form data.  Causes all form elements to be reset to their original value.

 */

$.fn.resetForm = function() {

    return this.each(function() {

        // guard against an input with the name of 'reset'

        // note that IE reports the reset function as an 'object'

        if (typeof this.reset == 'function' || (typeof this.reset == 'object' && !this.reset.nodeType))

            this.reset();

    });

};

/**

 * Enables or disables any matching elements.

 */

$.fn.enable = function(b) { 

    if (b == undefined) b = true;

    return this.each(function() { 

        this.disabled = !b 

    });

};

/**

 * Checks/unchecks any matching checkboxes or radio buttons and

 * selects/deselects and matching option elements.

 */

$.fn.select = function(select) {

    if (select == undefined) select = true;

    return this.each(function() { 

        var t = this.type;

        if (t == 'checkbox' || t == 'radio')

            this.checked = select;

        else if (this.tagName.toLowerCase() == 'option') {

            var $sel = $(this).parent('select');

            if (select && $sel[0] && $sel[0].type == 'select-one') {

                // deselect all other options

                $sel.find('option').select(false);

            }

            this.selected = select;

        }

    });

};

// helper fn for console logging

// set $.fn.ajaxSubmit.debug to true to enable debug logging

function log() {

    if ($.fn.ajaxSubmit.debug && window.console && window.console.log)

        window.console.log('[jquery.form] ' + Array.prototype.join.call(arguments,''));

};

})(jQuery);