User Hide PC from Domain

Is it possiable for a user to have hidden his pc from so that I can’t see it from the server. I can see if from server mgr (NT4.0 sp 6a) but when I click on it, it says “the remote computer is not available”. I know that he is here and that is the computer name. I can’t even see it in DameWare. Is there something he can do to cause this?