RAM Problems...

[Bullhead]

yeah, if the sticks fail in slot one with that memtest program, but they pass fine in your roommates pc then the mobo is definately bad (bad mem controller in that case). If they both pass, but it only detects mem in dimm 1, then the second channel is likely fubar. Either way, I suspect you need a new mobo MSI's new nforce2 line is a great line of boards, and can be had real cheap (~$80-90 online). If you can afford it, I'd HIGHLY recommend the ABIT I have, it's a solid, feature-rich board, and currently sells for around $115. You won't even need a soundcard with it!

[Bagginses]

Alright, I ran memtest86 over night with the 512 in the first slot and the 256 in the second, it only identified the first and the test passed 19 times...

-Bagginses

[Bullhead]

I'd still say the dimm slots are bad, that's my 2 cents.... like I said, maybe try just putting a stick in dimm 2 or dimm3, with nothing in one, see if it detects 'em. If not, it's likely bad. Kinda hard to say for sure, but it certainly sounds that way....