Avoidance of more than one signon

Ladies and/or Gentlemen:
I have a Win 2000 Server network and I want to know a way of avoid that a user can sign on more than once simultaneously, that is signing on in more that one machine at the same time. I know it can be done in UNIX where you can set a limit of only one signon at the same time for a defined user, but I?ve got to do the same in a Win2000 server network.
I will apreciate your help in this matter.
Regards: Jose Y Solano