This week I needed a particular VisualStudio 2005 project template called "ASP.NET AJAX-enabled Web site" and I could not get it to show up. Here is how I fixed it. You might also find these instructions interesting if you are simply trying to use Ajax in VS2005.
Whalla! VisualStudio 2005 is now Ajax enabled!
As a note, I tried installing all of these things in all different
orders and it never showed up. I had to uninstall to fix the problem. So if you are having a lack of Ajax, give it a try.