Here's a little poser that I have run across a few times. You get
Could not load file or assembly 'System.Web.Extensions, Version=1.0.61025.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' or one of its dependencies
after loading the Componentart 2007.1 code and trying to run the site for the first time.
The answer is to install ASP.NET AJAX 1.0. I read somewhere else that you need to make all the characters in the publicKeyToken (31bf3856ad364e3) uppercase, but I can't verify that.
Note:
I was able to verify that you don't need to do the 'uppercase' thing noted above, but you do need to 'restart' the application. Any edit to web.config will achieve this.
As always, comments are welcome.