UG, I have the same problem, however I have both Vista and XP on the same machine and both crash when I watch videos. XP however does it less often. I narrowed down the culprit to Nvidia, but in my case I don't know if it is the motherboard (I have a 780i) or the video cards (8800GT x2).
As far as I know, the 650, 680, 750 and 780 chipsets from Nvidia had lots of problems. I am waiting for prices to go down before I upgrade to a 790 which is much more stable (and DDR3).
Updating drivers for both (chipset and video) reduced the amount and crashes, and I have been working with almost no crashes for 5 months. The other thing that I realized, is that it crashes when I load more than one video, so for example, if I have a playlist, when after the second video it might crash in the middle of the second, or third. To solve that I use Windows Media Player classic, and I close the software before I open a new file. (WMPC opens really quick)