I just started a new position where we are using VS2005 and .NET framework 2.0. Which version of the AJAX control toolkit should I download?

In your case you should use toolkit version '20229' which is the latest for .net framework prior to 3.5.

Here is the link 'http://www.codeplex.com/AjaxControlToolkit/Release/ProjectReleases.aspx?ReleaseId=11121'

 Forgot to include that you should pick 'AjaxControlToolkit.zip' which targets .net frameworks prior to 3.5, and u should see there are seperate version for frameword 3.5.

Thanks for your quick response!