Just installed VS2008 on my laptop (has Vista Home Premium) and was having problems with putting the Ajax Control Tool Kit items on web pages. Come to find out it was the wireless mouse that I was using. I had to uninstall the wireless mouse software and disable the UAC (User Account Control).
This was after exhaustive efforts to figure out why it wouldn't work.
Thanks to several sites that pinpointed this issue.
http://www.west-wind.com/WebLog/posts/9932.aspx
http://www.west-wind.com/weblog/posts/10641.aspx
http://support.microsoft.com/kb/913405/en-us
