I have a Gateway LX4200-01e which was sold with a 300 watt power supply. After installing my BFG Tech nVidia Geforce 7600 GS OC (Core speed 420mHz) and running RivaTuner with the GPU monitor gadget on the Windows Desktop Gadgets, I notice that the temperature of the graphics card is always around 70C when idle, and 80-90 when gaming to watching TV through my TV Tuner.
After calling BFG Tech and asking if these temperatures were normal, they told me to check the wattage on the power supply, and I found out it was a 300 watt power supply, the customer service person said that this graphics card needed at least a 350 watt power supply.
Is it fine to continue using my Nvidia Geforce 7600 GS OC even though it's running at such high temperatures?
The factor cooler seems a bit small and it wouldn't surprise me if it had 70C idle temps to be honest. The 80-90C load temps seems normal though.
As far as your PSU, I wouldn't worry about it, the 350W is the minimum recommended specs. That includes the whole system and they assume a common setup with a buffer zone. If you had a quad core and two extra hard drives, it would probably make up for the difference. My buddy has a Dell with a 305W PSU and came with a factory 7900GS. So I wouldn't worry about it.