Crashing

My system seems to be rather unstable lately. I think I have tracked it down to something in the display chain. Either the nvidia drivers, or the nvidia card (integrated) itself. The system can record for hours on end, and I can watch dvds (from the dvd) and movies (stored on the hd) with no problems. However, as soon as I try to watch something in HD, I get kernel oops' that seem to start at the nvidia drivers, and cascade to everything else. I have to reboot to heal it. I have tested the memory extensively (memtest86+ for over an hour), and gone back to the previous driver. No luck. I guess it could have something to do with the kernel. I am not sure whether my next step will be to buy a standalone card, or to upgrade to feisty. Both have their pros and cons. But not being able to watch any hd stuff is getting old fast.