i use Winxp Pro on my home comp
win98se on older comps

Red Hat on one of my old old machines

use winXP pro on my desktop comp at work
use win CE on a panel industrial PC to test softwares

use win2k pro and winxp pro to test softwares in the lab...
the machines in the lab are dells and HPs
dual Xeons and singles P3's
some are P4 2.53GHz's
decent...