for one i will say, never go cheap on a PSU, for what little load you have, an Antec Earthwatts 620W would work.. this is what i have at work right now on a 620W earthwatts
i920 @ 3.8Ghz
12G of ram
1 x 640 WD
2 x 750Drives in raid 0/1 in matrix raid
Areca Raid card with 2 x 1T drives in raid 1
1 x LG BR burner
2 x ATI 2600XT's not in crossfire
most PSU calculators thought were often WAY off because they dont keep updated with recent power requirements.