Yeah I think you'll be ok. My dad's PC had a 300 watt PSU with a GeForce FX5500, 2 hard drives, 2 cd drives, a p4 2.4ghz, gig of ram, and 1 fan at the back.
I got a 250 watt PSU powering another pc with a 1.8ghz athlon xp, radeon 9550, 512 megs of ram, 2 hard drives, 2 cd drives.