That's ridiculous unless you're building an equally ridiculous gaming rig. (And of course the wattage rating is not the thing to look at)I wouldn't build a machine now with anything less than a 1000W P/S. Too much is not a bad thing, but too little will be.
I rebuilt my machine several months ago - A biostar mb, athlon ii x3 - 3.1ghz, 4gigs ddr31600 and a Radeon hd5700. Still using the 430watt Earthwatts from the previous build.
Each processor can use upto 100 watts
Each graphics card can use upto 100 watts
The motherboard will use upto 50 watts.
Memory modules and disk drives count 10 watts each.
Most systems will be in the order of 300 watts peak.
It's best to have a power supply rated 1.5x - 2x peak power usage. So 450-600 watts is perfect for most systems.
A psu with too low a rating will be strained. One with too high a rating will be dreadfully inefficient.