Windows Presentation Foundation (WPF, aka Avalon) has a known bug recently that caused a black window appears instead of a normal Avalon window. The problem occurs because Avalon executing SSE2 instructions on non-SSE2 capable processors and trashing FPU stack!
I discovered this bug when using WinFX December 2005 CTP running on Windows XP. I'm using an AMD Sempron 2500+ which doesn't support SSE2 instructions yet. I thought there's something wrong with my WinFX installation, so I decided to reinstall WinFX but it still happened. When WinFX January 2006 CTP released, I immediately installed it and wondered whether the problem occur. Well, it still!
Later on, I did googling and found this useful post (http://forums.microsoft.com/MSDN/ShowPost.aspx?PostID=157983&SiteID=1). According to Microsoft statement posted in here (http://lab.msdn.microsoft.com/productfeedback/viewfeedback.aspx?feedbackid=2e26e6c9-b7b1-4a5d-b661-d834330deb73), it will be fixed in February 2006 CTP (the feature complete WinFX).
So, I think I have to wait for a month... :(