There is a bug in our setup program that might be the culprit here.
When you install XNA GS 2.0 Beta, setup attempts to install into both VC# 2005 Express and VS 2005, if you have both. However, before XNA GS can be installed, you have to have the appropriate service pack (SP1) for the IDE. These are installed separately for Express and non-Express.
The bug is that if you have both VC# Express and VS, but only one has the SP1 applied, then setup will install XNA GS 2.0 into only the IDE that has the SP1 applied, but both will have the templates installed. The problem is that you cannot use the templates in an IDE without XNA GS 2.0 installed.
To see whether this is the case, go to the Help menu, and select About Microsoft Visual Studio (or Visual C# Express Edition).
If you do not see XNA Game Studio 2.0 in the list of installed products, then this is probably what happened.
To resolve this issue, download and install SP1 for VS 2005 (or Express) and then reinstall XNA GS 2.0 (there should be an option to repair/reinstall without uninstalling first).