Videocard
Your videocard plays the most important part in computers today.The cpu choice is almost unlimited,but heres the kicker.
My son plays counterstrike source on a p4 2.4 computer with a agp6800gt oc.He gets around 45 to 70 frames a second.Did I mention he plays on a 2.4 p4 with 4x agp.I get about 170 to to 230 frames a second,and I still get my butt kicked.
Processor speed matters the most when your playing poorley written games like gothic3,crysis etc.
Take a look around and you will find what games you cant play,people with the best pc in the world cant play good either.
I mean sure when they buy the core2 duo,and overclock the piss out of it.Me included.Then they go and buy two videocars and guess what?They still cant play crysis.They just simply turn all the options down and say hey i get 30 frames a second on high settings.
Every played crysis.
Now you are at a crossroads on your journey.The 8800gts are around 200 dollars in a bunch of forums.You can buy the core 2 duo on the forums for 70 dollars on up,then your gonna overclock the piss out of them,and still almost have the top of the line computer,for a real cheap price.So it doesent even matter the question you asked,for by now. Its cheap as hell just to go buy a good cheap board,core2duo,and a 8800gt off ebay or via the forums,then You will have a top of the line computer for almost nothing anyway,then you get to overclock the piss out of it and say,I atleast have close to the top of the line computer you can buy.