Limiting user logins

hey there! First of all, sorry if this is not the right thread to post this, but the thread’s description does include the word “login”, so…
Anyway, I’m using OpenSuse 10.2 (for reasons outside my control I can’t update, believe me, I tried…) and what I need is to limit user login: basically, I want to allow users to login only once at a certain time. That is, if a user is logged in already and someone else tried to login with the same user, it will be denied. I was looking into PAM, but that doesn’t seem to be the solution for this particular problem (also, I couldn’t get some nice explanations on how to do it, I did try…).
If someone could help me out here, it would be awesome! And, if someone is interested, this problem arose because I have several dumb terminals connect to a main server (using NComputing’s “wonderful” Linux solution - yes, the “” are on purpose) and I want to have only one user at a time logged in to the system (to avoid different terminals messing with each other cause they use the same user).

Thanks in advance!

Please clarify.

Do you require that only 1 user from many is logged in at any one time?

Or do you rquire that each of many users can be logged in at one time, but each user can only have 1 session at any 1 time?

I read your description both ways.