Hmmmmm...
First off... go Nvidia... f*ck ati... I swear i have had nothing but horrid luck with ati... they are not bad but man bad driver support...
If I were you Id go with a dual core. They are much cheaper now and pack a punch. Quad cores are a bit expensive but for 500 - 700 go dual core. Something like and E6550 or simular.
E6550 from Newegg...Third... Motherboard. Go with a 680i. They are the previous high end gaming boards from Nvidia but now trumped by the 780i boards which are expensive which in the end makes the 680i's cheaper.. I own a 680i and love the hell out of it. Many options. I got the EVGA 680i SE which cost more but you can get one of these which will do just as good but less options. Also you have to get DDR 2 800 Mhz ram only.
XFX 680i MoboRam.. Get OCZ, Patriot, Crucial, or Corsair. They are among the best gaming ram and DDR2 is cheap now... I have this ram and am very happy with it, damn fast and good for sli systems...
OCZ RamPSU, you have to get another powersource when you get a new mobo... dont ever NOT buy a new one when you upgrade. You will destroy your equipment.... Depending on what card you buy lets say an 8800. Dont go lower than a 600 W Psu. If ya get something more mid grade go with something like 400 W. But its worth it to spend the extra and get at least a 600 W... here is one..
Ultra 600 W psu..I think psu prices have gone way the hell up for some reason.. got my 600 W for $50.... odd...
Last thing is graphics card... if ya want an 8800 go with the new GT, its the cheapest, or you got the 8600 or you could go ATI.... they have the 2600 and 2900 and above... If I were you though Id go with an 8800 GT or GTS. Great cards for the money.
8600 GT video card 8800 GTS 320 MbDepending on if you have a case or not (if you do) all you have to buy is the mobo, cpu, ram, psu, and graphics card. If you already have a SATA II hard drive or sata 1 you are good to go. If you have the old IDE cable kind then you are going to need a new hard drive too.
A hard drive cost Your cd or dvd drives are all the same unless it is the old IDE or the newer SATA. You wont know the difference in speed in any way. The 680i mobos have the ide interface for the older ones so dont worry too much about those.
If you need a case go with a Mid ATX case for your needs. Here is an example...
Ultra Case...As it is with everything else you pay for what you get. DO NOT skimp on the motherboard!!!!!! That is your heart of the pc! Also DO NOT skimp on the psu... as you can fry your mobo with a cheap ass one...
Be as cheap as ya want on the case!!! LOL... unless you are running an 8800 then you need proper ventilation for the indsides..
Hope this helps.
Bumblebee