With your basic system, I don't think you have to worry about the power supply too much.
With my Antec 300 Watts power suppy I have:
ASUS P4P800 DLX
Intel P4 2.4C oc to 3.0GHz
2x256 MB 3200 DDR memory sticks
ATI Radeon 9800 oc with bios to 9800 Pro
4 hard drives: 1 15K scsi, 1 10k scsi, 2 7200 IDE
1 DVD+RW burner
1 scsi cd+rw
adaptec 29160 scsi card
Winfast TV2000 dlx tv turner card
1 firewire card
1 usb 2.0 card
5 extra case fans
Everything stable with a mere 300 watts antec power supply. Higher is always better but if I can load my system with everything I have then hey, a 330 antec should work just fine for you.