NVIDIA recommends at least a 350w PSU with a 6800 series.
Most importantly your PSU shuold have at least (1) 12v rail at 20a+
With out a strong enough rail, this will cause serious system instability.
Not to mention you've got a P4 3.2Ghz, probably prescott.
If you're system is overheating you need to address this issue right away. There are several things to consider.
1.) CPU Cooling - Check the Heatsink and fan, most likely it's loaded with dust. This needs to be completely cleaned. Dust will insulate the HS and seriously hinder heat dissipation. Dust also puts alot of unnecessary wear and tear on the fan. If worse comes to worse, consider buying an aftermarket HS & Fan. (Zalman, ThermalTake, Vantec) would be popular choices.
2.) System Cooling or Case Cooling - Again check the case for dust. Dust is an electronics nightmare. Due the electromagnetic field that electricity creates, every dust particle in the room will find it's way to your PC's internal components. Secondly, check all case fans, make sure they are clean and running properly. If it's possible you may consider adding another one. Poor wire management is also a factor, a birds nest of tangled wires can decrease airflow.
3.) Videocard cooling - Most HS & Fans that come with videocards are fine for standard use. More intense usage such as extended gaming and overclocking, will render the stock HS&Fan less then par. Consider aftermarket cooling, one preferred cooler would be one from "ARCTIC Cooling" The Assembly of the HSS & Fan allows direct exhaust of heat from the GPU to be blown directly outside the case through a secondary PCI slot. Most stock coolers will dump the heat inside the case, putting the removal on the case fans.
4.) PSU - Most cases position the PSU inside the top portion of the case, which is open to the rest of the PC. Even with a PSU fan a, lot of heat is created and left inside the case. This heat is due to lack of efficiency. The lower the efficiency, the more heat that is created. Efficiency is totally percentage of AC input - converted to DC output. Average would be 70% - Excellent would be 85%
The remaining percentage that isn't converted or can't be converted is waste which is lost in the form of heat....