After installing Silverlight 3.0 tools with VS 2008 SP1 i was not able to open XAML options in VS 2008 IDE.
I was submitted a ticket in MS Connect website, and the fix is:
1) Close all VS 2008 instances.
2) Open VS 2008 Command prompt
3) Type : devenv /resetskippkgs
This is the fix for the problem by resetting all IDE packages.
Hope it helps.