Best performance supposedly requires a gig of RAM, a 3GHz (or equivalent) CPU, and a Geforce6800 or Radeon 9800.
I'm slowly going up .5x clock multi at a time while I test stability on my CPU. Although I'm hoping that since I'm currently running above AthlonXP 3200+ speeds, I should be able to run it reasonably well. I did have a chance to try the (horribly slow) alpha at one point (same graphics card, but an Athlon XP 2000+ CPU), so much debugging code there that I'm sure the full release should run as well as I want it to at 1024x768 on my 19" monitor.
Intel Q9450 @3.2GHz, Gigabyte GA EP45-UD3P, 4 x 2GB G.Skill @4-4-4-12
Antec P160SW case (modded), Xigmatek 750w PSU
3x 500GB (RAID-5), , OptiArc 7200S, ASUS E818A3T
Creative X-Fi XtremeGamer, Hauppauge HVR-1800, Radeon 4890