I just got finished upgrading the build of Windows Vista on my tablet (was running the February CTP, now running a much newer version). The M200 only has 32MB of video memory with an nVidia Mobile 5200 video card but it's showing Aero Glass. Sweet -- I didn't think this was supposed to work on older, less powerful video cards. Let's hope this isn't an anomaly. 
[5 minutes pass...]
It installed *all* the drivers except one this time (I think it's the IR it can't find) -- I think we are turning a corner with Windows Vista. I've had a bear of a time getting the tablet to be happy with Windows Vista, and typically ran into mucho problems right off the bat. Everything seems perfectly normal.
[5 minutes pass...]
I installed Windows Vista Ultimate and am now using Windows Media Center with the Tablet PC pen.
Oh, this is SOOOOOOO cool...!