ASP.NET V1.0 and V1.1 have no explicit support for this technology (AJAX). Although they provide basic ways to manipulate script blocks, there is no easy way to incorporate more advanced techniques such as asynchronous client script callbacks.
With the upcoming release of ASP.NET V2.0, however, Microsoft focused on useability. This is evident when implementing common tasks and more complex technologies. In fact, ASP.NET V2.0 contains out-of-the-box support for asynchronous client script callbacks and provides a fairly simple way to register the callback methods, invoke them, and handle any associated errors.
Paul Glavich has posted how to use ASP.NET asynchronous client script callbacks without the need for add-on libraries. He’s also included source code on how to acomplish this. I’m going to have to take a look at this.