I have looked at a few of those online power supply calculators and they all seem to say i need 500-550 watts. I have a tendancy to keep the cpu pegged at 100% useage for a good chunk of the day. from gaming and making copies and compressing dvds and that sort of thing. Dont think it would be a good idea to get a power supply that just barely has enough power and spends most of its life working near 100% pretty sure that would just kill it faster then normal.
Also tend to do things like run the OS off the first drive play a game off the second while listening to music thats onthe third drive. So all three drives will be working at once. Would rather have extra power then not quite enough. Better to be safe then sorry and all that. And i could still have a little room for expansion. In the next year or so i would like to upgrade to a dual core processor and board. And most likely a better video card at some point after that. Doubt i would ever bother running two video cards though. I had a antec 550watt for the last few years in it and it seems i have worked that thing to death. at least i hope thats the problem or this is going to be a lot more expensive of a fix then i had hoped.
I am currently looking over reviews for the ocz gamextream 600watt
OCZ OCZ600GXSSLI GameXStream 600-Watt ATX Power Supply - SLI-Ready, SATA-Ready at TigerDirect.com
Just from looking over the forums for them it seems there answer for any problems is hey we will send you a new one. Sounds like a pretty good company as far as warrenty policy goes.