Thanks for the suggestion on the memtest. I ran it and it found no errors, didn't freeze or anything. Seems like the memory is fine. My old power supply was an Ultra 550 watt one, I bought a master cooler 460 watt one to replace it. I would assume that's more than enough to power what I have in the computer which is just two drives, cd/dvd drive and an MSI 4670 video card that doesn't require a power connector from the power supply.
I still have not run those tests on my second physical drive to see if it freezes my computer yet (defrag, WD Dianostic, checkdisk). I'll keep you posted.