Howdy,
From top of my head:
<script type="text/javascript">
var requestManager = Sys.WebForms.PageRequestManager.getInstance();
requestManager.add_initializeRequest(IntializeRequestHandler);
requestManager.add_endRequest(EndRequestHandler);
function IntializeRequestHandler(sender, args)
{
// this function will be called
// before async request is executed
// do soemthing here
}
function EndRequestHandler(sender, args)
{
// this function will be called
// after async request is completed
// do soemthing here
}
</script>
Hope it helps