ASP.NET AJAX is a free framework for quickly creating efficient and interactive Web applications that work across all popular browsers.

ASP.NET AJAX is built-into ASP.NET 3.5. It is also available as a separate download for ASP.NET 2.0.

With ASP.NET AJAX you can:

* Create next-generation interfaces with reusable AJAX components.

* Enhance existing pages using powerful AJAX controls with support for all modern browsers.

* Access remote services and data from the browser without tons of complicated script.

* Take advantage of the improved efficiency and ease of use in Visual Studio 2008, with its built-in support for ASP.NET AJAX, improved JavaScript support, and a new Web page designer interface.

You can download the necessary components for asp.net ajax from http://www.asp.net/ajax/

Consider the following steups to configure ajax on your asp.net 2.0 applicaitons.

1. Download the neccesarry dll

2. Put the dlls on the bin folder of your web application.

3. Configure the we.config file.

4. Add controls on your toolbox.

4. Drag and drop the ajax controls and thats it, now you can experience the ajax experience without any pain.

Click Here to  download the sample code for ajax asp.net application.