Windows is multi alot of things, but not really a multi-user platform in that sense of the word unless you use Terminal Serices. Win 2000, XP and 2003 come with 2 user license version of Terminal Services.
Without using Terminal Serices:
Multiple users and admins can login and access information at the same time. Print at the same time etc.
Multiple admins can adminstrate at the same time.
A single user or admin can have multiple programs running at the same time in a single user session (VNC or sitting in front of the server)
ONLY a single user session can be running in other-words.
With Terminal Services or Citrix multiple sessions can be created. That eats up system resources a bit.
Here's a link to start learning about it:
http://www.microsoft.com/windowsserv...lt.mspx#EBBAAA