It's an Asus 8600GT 256mb. He only has a 300W power supply, but I saw online that alot of the 8600s will run on that, and thats including some ridiculous "Intel Core 2 Duo Extreme" processor on the system. I can't seem to find any recommended power supply for this card, but the guy at the store said it'd probably run on a 300W and that there was no chance of any damage coming from it.
I guess I should probably explain here that a couple years back my cousin got a videocard installed by futureshop. Apparently he didn't have a big enough power supply in his system and it destroyed the whole computer. That is why i'm so paranoid about this (I actually have no proof that this was the reason, but this futureshop had to replace his machine, im assuming it was at least semi-truth)
He said the "worst case scenario" is that the machine won't turn on at all, in which case just remove the card and go back to the old one (integrated 6100) until he can get a new power supply. I realise it depends alot on what he has in his machine, but it's not that much. Athlon 64X2, 1 hard drive, 1 wireless network card. The hard drive I believe is a 5400rpm. I also got him a gb of ram (pc3200, if it matters) that will bring him up to 2gb, is there any real risk of breaking anything?