The specs:
AMD Ahtlon X2 4800+ clocked at around 3GHz
HD3870 512MB GDDR4, might OC to around 800/2500, depending on if Vista likes RivaTuner.
3GB DDR667 CL5
nForce 570 SLI mobo
From my experience, the ATI GPU client uses just as much power in Vista as in XP, so I'm not sure if it would be worth the troubles with Vista on it (Many of the games I/my friends will play on it occasionally aren't too fond of Vista)
I haven't used the ATI client in a while, though, so maybe things have changed? Care to enlighten me a bit?
