AMD Athlon64 3200+ (2 GHz, single-core)
2 GB RAM
GeForce 7600GT 256MB
ASUS SLI mobo
Prior to my current Linux distro, it was running Vista. Okayish performance, but had issues with lackluster drivers and bloat.
Currently runs Ubuntu 7.04 (32-bit), with XP running in VMWare for the (rare) occasions I must use Windows.