In my previous post, I only suggested the video card to get thing started. I spent some time matching up equipment for you and this is the very best, in my fairly informed opinion, that $500 can buy:
GeForce GTX 260 ($179.99 after $20.00 Mail-In Rebate):
Build your gaming computer around your video card. This card has come down $50 since my first post suggesting it. The GTX 250s are comming out now, but early benchmarks show that this guy is the king.
GIGABYTE GA-G31M-ES2L ($52.99):
Has on board video (backup), audio, network card and is reputable.
Intel Pentium E5200 Wolfdale 2.5GHz 2MB L2 Cache ($72.99):
Wolfdale in sheep's clothing
. A simple bios tweak will have this running at 3.2GHz with Intel Heatsink/Fan.
G.SKILL PI Black 4GB (2 x 2GB) DDR2 800 ($44.99):
A gamer needs gaming RAM! 4-4-4-12 timings at this price?
Seagate Barracuda 7200.11 500GB 7200 RPM 32MB Cache SATA 3.0Gb/s ($64.99):
Your new motherboard has the ability to use a SATA2, 3Gb/s hard drive. Dont even think of using your ATA133 drive on your new machine. You need to match the technology on your new computer, to avoid bottlenecks.
Rosewill RP550V2-D-SL 550W ($59.99):
The GTX260 needs at least 500W PSU. This power supply is stable and quiet. The stability of your system depends on a very good PSU. During gaming, the computer is taxed more than at any other time, so this is something you definately want to invest in. It has some blue LED lights on it though and intake fans on the top of the PSU, so take care installing it.
Thats $495.94 without shipping, which should be around $15, but rebates are $20 from what I can tell.
Your case will work just fine, btw. Might be a bit tight, but try it. You can always run out to a local shop and pick up a case you like the look of.
There is something else that I wanted to bring your attention to however. Guessing from the specs of your previous computer, I'm guessing you're sitting in front of a cicra 2002 CRT monitor. All of your hard work building this new gaming machine will go completely to waste, unless you invest in a brand new, widescreen LCD monitor. After all, it is your window to your computer:
Acer X223Wbd Black 22" 5ms Widescreen LCD Monitor ($169):
Acer P243WAid Black-Silver 24" Widescreen LCD Monitor ($259.99):
With LCD monitors you need to keep your eye on its natural resolution, for this one, its 1680 x 1050. You will get the best image quality and response time, when running games at this resolution. Most games should support this directly. If they dont, do a quick google search for the specific game and resolution for suggestions on how to enable it. Sometimes, you need to add the resolution manually in the game's .ini file - but thats about it.
When buying a monitor, I would advise looking into it very carefully. Its something that tends to stay with your for a long time and its also the one thing that reflects your computer's abilities and quality. If necessary, wait a month or two and buy the very best you can afford - You should never go for the cheapest option, when purchasing a monitor.
I will be overhauling my very very old computer soon also, and this is definately where I'll be starting from.
If you want some very well informed reading material, go over to Tweakguides and read
Koroush's Hardware Confution 2009, where he explains in detail why he chose each and every one of the computer components he put in his new 2009 machine. (That guy is like gospel for me).
Ow, and you will have to run Vista or Windows7 on your new machine, so that the games have DirectX 10 support - its an amazing difference.
Good luck, Spock! Post back what you've decided!