Blue pointed you to Toms Hardware it's a great reference site.
Agree completely with Joe - I stay with Win2K and Linux; XP is a no-go for me because of microsoft's fetish for policeware. Note: ms is primarily focused on DRM, not on a better o/s. I'm also staying FAR away from Vista. See:
http://www.symantec.com/avcenter/reference/ATR-VistaAttackSurface.pdf
I like AMD processors - the 64-bit work exceptionally well, and dual-core will be my next build. Two things to watch out for: Heat and Noise. Get a big mother power supply - you'll need it with the graphics requirements you've described. Consider temp-variable fan speed control to keep the racket down.
You can't have too much RAM.
I also really like drive racks - they allow you to build different system configurations just by swapping hard drives. Really improves system flexibility since the same hardware can do radically different things without configuration compromises.