I'd be concerned about the PSU. That's enough PSU if you have a plain vanilla non-gaming vid card in there, but not for a 6600GT. You might get away with it because Antec PSUs are quality units. My LAN party rig ran just fine with a 350w Antec PSU and a Radeon 9800 Pro which is a pretty power hungry card.
You can try it but if you get mysterious lockups or reboots while gaming, my first suspect would be the PSU.