My main machine Athlon XP 2500+ OC'd at 3000+ and my only borg - a Celeron 2.2 GHz is running Windows XP Pro.
The rest of my boxen are running on Windows 98 SE. :)
I just started folding and have my primary system as well as a borged system.
Primary System: Athlon XP 2500+
Borged System: Celeron 2.2 GHz
Hope this helps.