600w coolmaster cxi series
intel quad core2 2.4 ghz
for budget, cant really say maybe $100. if its mostly just the GPU to upgrade. what is the best he can get for the current mobo, processor and psu?
As long as your motherboard (I'm guessing Intel 945? 975?) has PCI-e x 2.0 you should be able to run any graphics card you want. If you want the best bang for your buck right now - no question it's the Sapphire Radeon 6850. You can find them for about $160 - $170 on Newegg - the Flex model with Eyefinity will run a bit more.
If you wanted to spend a bit more I'd recommend going with a EVGA Geforce GTX 560.