Driver infinite loops - ATI and nVidia

Been getting alot of these errors lately. Started out a couple weeks ago with my Sapphire Radeon HD3850 PCIe. It mostly would happen during Call of Duty 4. I would either get a BSOD, a VPU recoverer error, or the system would just hang with no escape except a hard reset. When I would get the BSOD, most of the time it would say that ati2dvag stopped responding and got stuck in an infinite loop. Could not find any fixes anywhere, so I just took the card out of the system. At that time my system was:

ASUS M2N-SLI Deluxe (with latest bios)
AMD Athlon x2 6400+
2GB G. Skill DDR2 800 (single channel)
HD3850 mentioned above
500GB Seagate Barracuda SATA 300
500W Raidmax PSU (came with the case)

So then I decided to put a new HDD in the system (WD 320GB SATA 300) with a fresh install of Windows XP. Figured I'd give the 3850 one last chance before I RMA'd it. Wouldn't you know it worked like a charm......for about a week. Now back to the same familiar crashes. So I took it back out and RMA'd it. I uninstalled all ATI drivers and ran Driver Cleaner Pro in safe mode, put a eVGA nVidia 8800GTS 320MB in the system and all was well......for a couple hours. Now I'm getting freezes and nv4-something or other is having issues and stuck in an infinite loop. Now this time it only seems to be with Far Cry 2. CoD4 runs just fine for extended periods of time. I don't get it, why am I getting all these infinite loop errors, and with both chip manufacturers? Its getting really frustrating!! And since I know somebody is going to say its probably my PSU and ask what its story is, I know it is a bit underpowered. It has a single 12V rail at 22A. But I refuse to believe that is the issue, as I had the same 8800GTS running on a PSU with, get this, 13A on a single 12V rail! I know thats actually really stupid, but it was temporary. Had a lot less problems then, though. So what do you folks think? Do you need more info? I'm at a loss.