I take it u got the card, but u should be fine with a 400w psu... the 7600 is actually a card reknowned for running cool and at low power. In my internet pc here I have a 7600SE 512mb (silent edition- no fans :s) which i picked up for near to nothing. This PSU is a cheap 450w and all is fine...
To give u an idea what u will be able to run on this card I used to happily play oblivion on this pc @1024x768 pretty much maxed. In fact ull get away with most games but the most recent at a lowish res like the above. (I run wow in 1280x1024 maxed, and same for most HL2 games (except newer titles with the shading.. then its 1184x)

oh and the hellgate demo seems to run 'ok' for me, with 1.5g or even a gig atm, settings maxed @ 1024x768 (without aniosotropic or trilinear but meduim AA) not saying u dont need to upgrade for it but its actually a nice peice of code and runs well... addictive too
No Bioshock for me tho- the demo staggered along maxed and theres no way i wanted to see rapture in 800x600!

Bring on my new rig!!!