If you are a web developer just evaluating ASP.NET 3.5 and VS2008, I strong recommend you go grab VS2008 Web Express and the updated ASP.NET AJAX Toolkit. It is full of some really great AJAX controls for ASP.NET... It is a community driven open source project that Microsoft has put some full time developers on to seed. I love to use these controls in my application building and demos... I am sure you will to!
Please check out the sample website page to see all the controls in action!