I would really suggest waiting for DirectX 10, but if you WANT the PC now here is what $1000 will get you now, if you want to spend $1,000 INCLDUING a DX10 card...then I'll respond again. Are you in the market for a new monitor as well? that will need more tweaking as well...
First Things First, Hurry up and get this if you want Windows Vista.
Windows XP Media Center Edition with Upgrade Coupon to Windows Vista
Hurry up on this one, you can't beat that...two Operating Systems for $110, I know it sucks paying $110 for Windows XP at this point...but you get Windows Vista which will retail much higher.
http://www.newegg.com/Product/Product.asp?Item=N82E16832116171
All The Top Rated Products here.
Intel Core 2 DUO Processor @ 2.13 GHz - $220
Motherboard with 8GB RAM Support with Onboard Video - $150
http://www.newegg.com/Product/Product.asp?Item=N82E16813128018
2GB of DDR2 800 RAM (ONE STICK) - $305
http://www.newegg.com/Product/Product.asp?Item=N82E16820231121
DVD+R/DVD-R DL Burner - $45
http://www.newegg.com/Product/Product.asp?Item=N82E16827131039
DVD Rom Drive - $25
http://www.newegg.com/Product/Product.asp?Item=N82E16827101131
ATX Case - This is pretty much your choice right here...I mean I don't know what you like so I won't recommend this one...but expect it to run about $120. Make sure it comes with a 500 Watt Power Supply...you are going to need it. Make sure it also comes with fans.
120 GB Hard Drive - $77
http://www.newegg.com/Product/Product.asp?Item=N82E16822148106
Keyboard & Mouse - $20
Just pick whatever you like, I prefer Wired
So what are you looking at here...$1,072 with Windows XP...
$962 if you already have Windows XP. It's going to be basically Impossible to get a nice PC with a DirectX 10 Graphics card in the near future, but what u have here is an option to build for the future without having to switch out RAM Sticks or Video Cards. I know the RAM might cost more now, but it's worth it as that motherboard can handle up to 8GB giving you a very good amount of breathing room for the future and the option to upgrade to the Core 2 DUO EXTREME in the future if you'd like.
I also STRONGLY DO NOT Recommend a Computer Company for gaming...when you build on your own not only is the experience fun (I'm a nerd) but the options to upgrade are much better.