dll
http://blog.rameshbhaskar.com/2008/12/05/re-compiling-the-ajaxcontroltoolkit/
For example, styles from that post for IE7 and Firefox would be:
.jasons_modalBackground {
position:fixed;
top:0px;
bottom:0px;
left:0px;
right:0px;
overflow:hidden;
padding:0;
margin:0;
background-color:#000;
filter:alpha(opacity=50);
opacity:0.5;
z-index:1000;
}
ModalPopup Demonstration
http://www.asp.net/AJAX/AjaxControlToolkit/Samples/ModalPopup/ModalPopup.aspx
http://blogs.visoftinc.com/archive/2008/03/13/Modal-UpdateProgress-for-UpdatePanel-Revisited.aspx