Cannot Find Ajax Controls in Visual Studio 2008

I started learning asp.net recently and when I try to add a script manager control on 开发者_StackOverflow中文版a new webform I don't find it or the ajax control section within my toolbox. I searched the internet for the answer but nobody is talking about this issue. I always get instructions for downloading an ajax library from codeblex but I think its not the same thing I am searching for. Also, I can find the ajax section if I click 'show all sections' on the toolbox but it is still inactive or dim icons only; i.e. it does not work.

How can I make the script manager control work?

i found out that my project was configured to run under .NET 2.0 which doesn't support using the ajax extension controls so i simply change my project framework to .NET 3.5 and everything work fine also i came to know that if i need to keep .NET framework 2.0 i must install the ajax extension for this version manually.