*Sigh*. UDawg created a sticky about this.... It's been stated time and time again. Nvidia lowered the wattage reccommendation from 480 to 350, although some people have been able to run at 300. IT ALL DEPENDS ON THE AMPS ( think A stands for that?) ON THE 12V RAIL!!! Check you PSU manual, or even better the back of your PSU. It should have a little graph thing like this 12v-20A or something with a bunch of more stuff like that. If your 12V rail is 18A or more (actually like 20 to be safe) then your good to go.
All depends on how many more accessories you have plugged in also. But a 20A on 12v rail is enough, my Antec True430 430Watt PSU has 20A on 12v rail, and has been runnning perfectly on a GT.