I just started ordering parts to build my cabinet, and ordered an AMD XP1700+, 256MB DDR Barebone system with case for less than $300.
I threw in a harddrive, CD-rom, and an ati rage fury video card, and I've been playing games all weekend. My main system for working on is a PII 800Mhz, 128Mb ram, and a geforce 2 video card. It ran all the games fine, with no degradation in play.
I can't wait to get the controllers in. Playing games on the keyboard is getting very uncomfortable. Major hand and finger cramps.
Daniel