I think you'll find I am right. I just tried to power a new system that had a 7800gt with a 450w psu with 25A on the 12v rail and it didn't have enough power for the dvd drive to work.
This was an amd 3200+ , 7800gt, Asrock Dual sata2, 1 gig ram 1 hdd 1 case fan 1 dvd burner 1 cpu fan...