How to Use the AJAX Control Toolkit for ASP.NET
The ASP.NET AJAX Control Toolkit is a shared source project built on top of the Microsoft ASP.NET AJAX framework. It is a joint effort between Microsoft and the ASP.NET AJAX community that provides a powerful infrastructure to write reusable, customizable and extensible ASP.NET AJAX extenders and controls, as well as a rich array of controls that can be used out of the box to create an interactive Web experience. This video tutorial will get you started using it. Take a look.