If you haven't downloaded the v1 release of XNA Game Studio Express yet then this contest may be an incentive. There is just a teaser there now because the contest doesn't open until January. But you or maybe some of your advanced students who are looking for a way to show off their mad game development skills may want to get the software now and start playing with it.
There is information about some XNA tutorials here BTW.
PS: It looks like Tom Indelicato, a friend of mine and an outstanding high school computer science teacher, is looking at using XNA GSE for projects in his Advanced Placement Computer Science class for after the exam.