I thought the same thing with my machine so here is what I did. the Windows 7 machine is triple booted with XP and Ubuntu 6.1 on three separate hard drives, so I downloaded memtest and tested for 8 hours in XP then I stress tested the video by running 3dmark 06 in demo mode for 3 hours. Suspecting a bad hard drive or cabling issue for the Windows 7 drive I also did a full sector check on the hard drive using Seagate Seatools. This machine runs rock solid in both XP and Ubuntu. Also my NAS does not have any compatibility issues with XP, Ubuntu, Mac Os X or Vista, as I have connected all of these OS's to it at one time or another. I believe hardware issues are ruled out.
A driver issue is still a possibility, but why would it just mysteriously start working again after I unmap my drives? I re-mapped them after about 6 hours of solid operation in Win7, and guess what 5 minutes later BSOD.
I am convinced this is a AVG or windows 7 bug.