Read up on peltiers at these two website. I got most of my ideas there anfd my systems work fine. How many people can say they have a P2-450 running 527 MHz at 100% FULL CPU load or will boot 558 MHz with Win98 in idle?:
Is your 350 Watt power supply a 12 volt power supply, what type of supply is it? (at, atx, switching, etc.)
At 12VCD your peltier should only draw about 3.6A. That is still an additional 43.2 watts that your heatsink has to dissapate. If you dont have too many devices in your system your p.s. should be able to handle an additional 3.6A, but at 12V your peltier is not going to cool even close to the rated delta T.
Generally Peltiers have been getting a bad rap because people are trying to cool the chip to 32F or below and on top of that are using watercoolers. I have found from my testing that going below room temperature will not get you much more in performance. If the payoff is 22 MHz (i.e 583 to 605) but the cost is cooling the chip to 32F, it's not worth the chance of condensation, run it at 583 at room temp and be done with it.
If you match a peltier to the chip then you can run at room temperature and not have a condensation problem. Don't go out and buy the biggest peltier you can find. A 40Watt (12V) peltier will cause condensation. A 30 Watt (5V or 12V) will not if used on a [email protected] volts. Also peltiers need a cold plate between the CPU core and the peltier unit. This can be made of 1/8" - 1/4" Copper or Aluminum. Lastly if possible use a temperature sensor on the cold plate so you can know if your going to have a condensation problem and NEVER run without the case cover on.