It will actually use very little power for the performance that you get.
At stock speed the E6600 (2.4GHz) consumes 52w of power. The X6800 (2.93GHz) consumes 66w or 67w. I estimate my E6600 @ 3.0GHz consumes about 70w of power at full load.
Off the top of my head, the 7900GS should consume about 55w max. Sorry for not providing links, but I feel kinda lazy at the moment.
You can go to www.xbitlabs.com many of their CPU and GPU reviews also touch upon power consumption just for those component. That's the site where I get my numbers from.
The typical hard drive uses about 14w of power. Power consumption basically depends on the RPM speed and the number of platter. The faster and/or more platters increases the power consumption. Each DVD drive will consume about 14w as well.
Each 120mm fan will draw about 6w of power at full speed. The typical 80mm fan will draw about 4w at full speed.
Assuming you are OCing your CPU to 3.0GHz and you are using the above components with three 120mm fans at full speed, your system should draw at most 171w of power on the 12v rails. That works out to 14.25 amps.
Off the top of my head, most 430w should have at least 22 amps or 264w on the 12v rail. If you already have a 430w PSU, then you should be okay, but it's always best to inspect the PSU's sticker. However, most PSUs list max peak amperage or wattage on the 12v rails, not the constant amperage/wattage.
If you are looking for a good inexpensive PSU then look for the Fortron 450w PSU which should sell for about $55.