I just noticed that the code name ATLAS is changed to ASP.NET AJAX before it's official release
click here to download the updated toolkit, enjoy
AJAX stands for Asynchronous JavaScript And XML from its name it seems that it’s a collection of technologies when we talk about it we don't talk certain type of code that you do to have AJAX but we talk about a set of technologies that we daily use in our applications but we don't mention its powerful use in the usability and user experience fields.
From my opinion I think that its growing name it will be the next step toward developing more rich UI web application that will provide users with more usable way of interacting with our web solutions.
AJAX uses a communication technology that depends on SOAP and XML to send and receive an asynchronous request/response to the server, plus presentation technologies (JavaScript, DOM, HTML, and CSS) to process the response
There is already a Class Library for the ASP.NET application to be able to use AJAX
For more information visit
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dnaspp/html/ASPNetSpicedAjax.asp