Hard drive:
http://www.newegg.com/Product/Product.aspx?Item=N82E16822136218 - meh, any old will do. These specific 640Gb ones use the newer 320GB platters instead of 250GB ones, meaning it's quieter and more efficient =)
Graphics Card:
http://www.newegg.com/Product/Product.aspx?Item=N82E16814102747 - Nvidia has been kicking ATI's ass for years, but they've made a spectacular comeback and currently the 4850 is the best card out there for the price. It'll rape earlier 8800GTs.
PSU:
http://www.newegg.com/Product/Product.aspx?Item=N82E16817171028 - Don't skimp on the PSU ever.
RAM:
http://www.newegg.com/Product/Product.aspx?Item=N82E16820141300 - Any old RAM is ok for what you will be doing =)
CPU:
http://www.newegg.com/Product/Product.aspx?Item=N82E16819116052 - Budget one, we'll get to this later
Motherboard:
http://www.newegg.com/Product/Product.aspx?Item=N82E16813128337 - bog standard, priced cheaper now that the newer P45 chipset is out
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Even with everything at stock, you'll have a very speedy machine. The weak spot is the CPU, but this is why we got the higher end motherboard. The e2xxx series CPUs aren't in fact pentiums as the name implies, but artificially slowed down run of the mill core2s. They are
identical to their double, even triple priced big brothers, except for less cache. The reason for the e2180 specifically is its 9x multiplier, and the reason for the higher motherboard is that it can support up to 1333Mhz, even 1600 Mhz if you're willing to push it on the FSB. The e2180 uses an 800Mhz FSB at stock, so with this board we have plenty of headroom.
the
e2xxxs are famous for being the biggest overclocking CPUs available out there, with more aggresive cooling you can literally double the speed, but with what you get (you'll get a standard heatsink and fan with the CPU) you can push it from 2Ghz to 3Ghz pretty easily just by increasing the FSB in the BIOS. If you have absolutely no idea what I'm talking about, get a nerd to do it for you, it's not that hard.
This ~$500 computer when put together and setup will beat the shit out of Nouman
& Anski's money flushing computers in pretty much every game out there