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Jeffz.Web.ModalUpdateProgress = function(element)
{
    Jeffz.Web.ModalUpdateProgress.initializeBase(this, [element]);
    
    var fakeElement = document.createElement("div");
    this._modalPopupBehavior = new AjaxControlToolkit.ModalPopupBehavior(fakeElement);
    this._modalPopupBehavior.set_PopupControlID(this.get_element().id);
}
Jeffz.Web.ModalUpdateProgress.prototype = 
{
    initialize : function()
    {
        Jeffz.Web.ModalUpdateProgress.callBaseMethod(this, 'initialize');
        
        this._modalPopupBehavior.initialize();
    },
    
    get_backgroundCssClass : function()
    {
        return this._modalPopupBehavior.get_BackgroundCssClass();
    },
    set_backgroundCssClass : function(value)
    {
        this._modalPopupBehavior.set_BackgroundCssClass(value);
    },

    ...
}

.modalBackground
{
	background-color : gray;
	filter : alpha(opacity=70);
	opacity : 0.7;
}
#updateAnimation
{
	color : Black;
	background-color : #ffffae;
	font-family : Arial;
	font-size : 8pt;
	font-weight : bold;
	line-height : 30px;
	height : 30px;
	padding-left : 5px;
	padding-right : 5px;
}

<jeffz:ModalUpdateProgess ID="ModalUpdateProgess1" runat="server"
    BackgroundCssClass="modalBackground" DropShadow="true">
    <ProgressTemplate>
        <div id="updateAnimation">
            <img src="animated_loading.gif" alt="Loading" />
            Working on your request...
        </div>
    </ProgressTemplate>
</jeffz:ModalUpdateProgess>