Re: power supplies
hmm it depends. It's going to be the Video card that will take the most power out of the system. These days I wouldn't go any lower than 450watt's if its a full fledged machine. Mines a 500watt's and runs perfectly. I wouldn't see for most computers why you'd need more than that, unles its powering lots and lots of devices like for instance a SLI board runing two video cards.
Even then, 500watts would probably be sufficent
Abit IP35 Pro / Q6600 G0 / Zalman 9700 / 8800GTS 640mb / 4x 2GB Corsair XMS / X-FI Xtreme M / 1x 1TB / Antec 900 / Logitech Z-5500 / Samsung 20inch