Please recommend Processor and Graphics card(s)

Basically I want to get the most out of this computer. I've posted another thread about some awkward problems I'm having, and since no one seems to know anything to solve the problem, I've decided to replace every possible non-working part.

I've already replaced the motherboard, and am now running an Asus P5N-D with a 600W power supply, 2x 18A,12V rails. Basically I'd like someone to recommend the best possible processor and graphics card set up for this motherboard under $1000. I am running Windows XP, and want to get the best possible gaming performance out of this machine. If there's a strong consensus for more pricey alternatives, I am willing to consider them, but of course I'm not made of money and would prefer the less expensive options.

Resolution is 1440x900 usually. My memory is at 2GB for now, can upgrade later if I switch OS's.. right now the most intensive game I play is world of warcraft, although I certainly want to be able to handle virtually everything I can throw at it.

Frankly' I'd spend some of that cash on a larger monitor first.