Note: I'd only recommend this list for purchase right now, today, as the AM2 is due out in ~3 months and the Intel Conroe is due out in ~6.
Note: This is assuming you are not going to be incrimentally upgrading anything besides the GPU in the next few years.
AMD Athlon X2 3800+ $296
XFX 7600 GT $209
OCZ 2 gig kit $142
Abit AN8 SLI $95
Creative Sound Blaster X-Fi music $112
Antec Lifestyle Sonata II $75 - case + PSU, though I doubt the PSU will be SLI ready. You may need an adaptor if you decide to go that route.
Western Digital Caviar SE16 250 gig HD $93
BenQ DVD burner $35
Logitech G5 Laser mouse $47
Keyboard $45 - fancy gamer version, your choice
Creative Inspire 5800 5.1 speaker set $60
Total = 1209
Not counting tax or shipping
A little over, but it would be a very solid system. 1k or under is very tricky to get a complete build for; more likely you want to consider a simple core upgrade in that range (CPU, Ram, MB, GPU.)