BUILD!!!!!!!
Although I'd wait for ATi Crossfire, you could get a nice gaming rig for pretty cheap. Here's how I'd budget:
-Case: Decent quality without power supply, at least 3x80mm fans, or 2x 120mm. Try to get some front USB and audio ports, possibly IEEE 1394 Firewire. If it doesn't come with fans that's okay, at least have them as options - you'll NEED the cooling. A nice Antec or Lian Li can be found for $80-$100, and if you look around xoxide.com, there's free shipping right now until June 12th! You can find the MGE Sidewinder there for $65, a steal imo.
-Power Supply: Do yourself a favor and get a QUALITY one. NO POWMAX. Spend about $60-$70 on a good 500W-600W PSU. There's the Aspire Chameleon on xoxide.com which goes for $70ish. OCZ makes great ones, and also at xoxide.com there's a rebate on X-connects.
-Case Fans: If you can find a good fan (brand doesn't matter much), snag it. For 120mm fans, look for at least 40cfm and 25 db, 80mm go for at least 35ish cfm and around 25 db.
-Processor: Gaming = AMD, office/work = Intel. I'd easily go AMD over Intel, better value. If you can, find a nice AMD Athlon 64 *VENICE* core 939 socket proccy. They're great, and on newegg.com they're around $160sih i believe. Venice cores clock better than other A64's and they'll easily go to 3700+ speeds from 3000+ speeds. For Intel, a 2.4C or 3.0E can be clocked to 3000mhz and 3500 mhz respectively on stock cooling, go aftermarket, and you're bound to go even further. Spend only $240 at the most.
-RAM: High quality OCZ, Corsair, or Mushkin. Spend about $180 for 1GB Dual Channel PC3700 or more. The speed at stock doesn't matter! You can overclock it later anyways. DDR400 isn't bad anyways...if you want DDR2, i'd lead you to OCZ methinks....not sure on DDR2.
-Video Card: A Radeon X800XL will run you $280 and kick ass. If you want more, look at the nVidia eVGA 6800GT. SLI sucks for 6600GT, and 6800GT SLI's are friggin expensive. Although ATi cards don't support pixel shader 3.0, they're still very competitively priced these days. Don't go over $380.
-Sound Card: Optional, depends if you want it. Shouldn't matter too much.
-Motherboard: For the socket 939s, I'd recommend an ASUS A8V-E. Good stuff, but look around, there's more to be seen too. Intel...well, who knows, there's tons out there. Shop around, post your results here, and we can give second opinions.
-Monitor: Samsung 710N for $220ish on newegg.com. The decent 19" are DAMN EXPENSIVE lol. I have a Samsung 710T, which utilizes the same technology as the 710N, just with swivelly stuff (great for LANs/transport). 17" should suffice, if not, a 19" 193P Syncmaster also from Samsung, a Dell ($650+ though for a good one that won't blur), or a BenQ (again, quite expensive) will do well. Samsung>pretty much everyone else so far.
Good luck, if you need more help, plz ask!