What are a few main differences between Microsoft's Windows NT, 2000
and XP?  Thanks very much.

I think this website will help you a lot:
http://www.tss.northwestern.edu/windows/compare_win.html
Title:
Which Windows operating system is right for you?

I've used all of those operating systems, but XP is more "user
friendly" than 2000 and NT.  XP was designed for hame and professional
use. I would chose this for a personal pc.  NT is designed for
servers.  Nt isn't very user-friendly, and only certain software will
work on it.  I would use this for a server.  2000 is the "bridge"
between xp and nt.  2000 has the server stability but has an "ok" user
interfacce.  If you want something for your home computer i would go
with XP.  If your working on a server or something NT will do fine for
a personal server but i highly recommend 2000 for a corparte server. 
I hope this helps, bamnet

NT 4 was completely perfect and catered toward people who really knew
what they were doing.

2000 built on the perfection but laid things out a little more
logically and made adminstration a bit easier.

XP took everything that was good and destroyed it all by trying to
make it idiot-friendly and just wound up insulting and frustrating
"power users."