Operation Silverlight (our game contest) is well underway. Someone is going to win a Zune, so get cracking!
I've poked around the dark corners of the Internet and found some Silverlight Game Tutorials that might help you out.
I'm not ranking them or judging them, just listing them for your enjoyment.
http://www.ddjsilverlight.com/
http://silverlightrocks.com/Community/blogs/silverlight_games_101/
http://laumania.net/post/PopTheBubble-Silverlight-game.aspx
Here's a great link that points to a bunch of Silverlight games:
http://blogs.msdn.com/cbowen/archive/2007/06/29/index-of-silverlight-games-most-with-source.aspx
Good luck and have fun!