Linuxeagle;
I have the same setup with Windows XP and a Linux server. What I did was set up each computer to have one administrator password (with all permissions) and one user password (with very little permissions). My users cannot access the control panel, chage their desktop picture, or install any programs. But the administrator can.
This is not done throught the Linux server. (If anyone knows how, that would be great). Rather it has to be set up on EVERY workstation individually.
Here is a link on how to set up the policies for only the USER on the Xp or 2000 machine, and not affect the Administrator:
http://www.jsiinc.com/subl/tip5600/rh5619.htm
Hope that helps. I don't know how to set policies from the server.