Ajax Question

[Microsoft Newsserver]

I am running ASP.NET 2.0 with Ajax.
I am invoking an asyncronous postback by invoking a button click which
triggers the async postback. This works fine, but I need to take into
consideration the success or not of the request.
//Pseudo Code.
__doPostBack( 'btnMyButton.......

alert('Thank you, your request has been completed');
OK, no what is happening of course is that the alert pops up before the
relative update panels are updated on the client.

I need to be able to

a.) Sync my 'Thank You' Message with the reuest being complete.
b.) Take into consideration that a timeout may occur.
Any constrcutive suggestions to do this would be greatly appreciated.

Thanks ....