Here is a very good ariticle about using performance/profiling tools in Visual Studio Team Suite to troubleshoot ASP.NET performance issue. Tess has described all the steps in this blog article:

 Using VSTS Test and Profilers to troubleshoot performance issues (low cpu hang)

http://blogs.msdn.com/tess/archive/2008/10/01/using-visual-studio-team-system-test-and-profilers-to-troubleshoot-performance-issues-part-1.aspx