SYSTEM REBUILD need advice

Its about time for me to rebuild my system soon within the next few months. The whole reason i want to rebuild is for the sole purpose of Unreal Tournament 2007. But considering it comes out begining of next year i might wait a little while. Anyways i just want some advice for what to get. I want the best performance i can get for probably about $400-500.
But i'm only buying a new motherboard, processor, and videocard(planning on it anyways) right now i have:

Abit k8t800 athlon 64
Radeon 9800pro AIW 128mb 256bit
AMD Athlon 64 3000+ 256kb cache
Kingmax (2*512) ddr 500

What would you guys recommend for motherboard, video card, processor?
Nvidia? ATI? SLI? (512mb/128bit OR 256mb/256bit video card) AMD dual core? single core? Gimme anything you know PLEASE!!!