Having migrated a few servers over to IIS7 I have started to realize the power of IIS7. I have debugged everything from a forwarded site fail to a .NET 1.1 site not work. One of the great posts to read that will help you start to troubleshoot isssues is from Mike Volodarsky
(Troubleshoot errors like a pro)
http://mvolo.com/blogs/serverside/archive/2007/07/26/Troubleshoot-IIS7-errors-like-a-pro.aspx