ModalPopupExtender

ModalPopupExtender

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