It's enough. I wouldn't really get too paranoid over this. Measurements from a 6800 uses like 5 amps on a 12V rail so your power supply should be more than adequate for that video card. Just make sure to use a dedicated plug directly from the power supply instead of off of another molex plug from another device.
I'm using a 7800GT which requires more power and I'm only using a 450watt power supply at these specs:
ASPIRE CONCORD ATX-MR450W ATX 450W Power Supply 115/230 V cUL, FCC, CSA, CB, TUV, CE, NEMCO, DEMCO, SEMCO, TC - Retail
Can't run any better.