A modified version of jDoubleSelect 0.3, altered to work jQuery 1.6.4 on optgroups with spaces

jquery.jDoubleSelect.js

/*
* jDoubleSelect jQuery plugin
*
* Copyright (c) 2010 Giovanni Casassa (senamion.com - senamion.it)
*
* Dual licensed under the MIT (MIT-LICENSE.txt)
* and GPL (GPL-LICENSE.txt) licenses.
*
* http://www.senamion.com
*
*/

(function ($) {
    jQuery.fn.jDoubleSelect = function (o) {

        o = $.extend({
            text: ""
        }, o);

        return this.each(function () {
            var el = $(this);
            var name1 = (el.attr('id') || el.attr('name') || el.attr('class') || 'internalName') + '_jDS';
            var name2 = name1 + "_2";

            groupSel = "";
            $(this).children("optgroup, option").each(function (i) {
                // Verify disabled or selected group
                if ($(this).attr("disabled"))
                    s = " disabled ";
                else if ($(this).find(":selected").attr("value")) {
                    s = " selected ";
                }
                else s = "";

                if ($(this).is("option"))
                    groupSel += "<option " + s + " class='jds_isOption' value='" + $(this).val() + "'>" + $(this).text() + "</option>";
                else
                    groupSel += "<option " + s + " value='" + $(this).attr("label") + "'>" + $(this).attr("label") + "</option>";
            });
            $(this).hide().after("<select name='" + name1 + "' id='" + name1 + "'>" + groupSel + "</select> <span>" + o.text + "</span>");

            $("#" + name1).change(function () {
                // REMOVE OLD ELEMENT, ADD NEW SELECT, BIND CHANGE EVENT AND TRIGGER IT
                if ($("#" + name2).length > 0)
                    $("#" + name2).remove();

                if (!$(this).find(":selected").hasClass("jds_isOption")) {
                    el.next().next().after("<select id='" + name2 + "' >" + el.find("optgroup[label='" + $(this).val() + "']").html() + "</select>");
                    $("#" + name2).trigger("change");
                } else {
					el.attr("value", $(this).val());
				}
            });

            $("#" + name2).live("change", function () {
                el.attr("value", $(this).val());
            }).trigger("change");

            $("#" + name1).trigger("change")
        });
    };
})(jQuery);

Changes made on b9b012 courtesy of "Alex"