How do you remotely find out out who is logged into a machine?

Hello,
I am a network associate for a small network of about 40 computers, but we also have a vpn connecting us to another office. I am trying to remotely find out who is logged into a particular machine. Is there anyway to do this? I tried using [nbtstat -A IP Address]but it only seems to give me the name of the machine and the domain name. Is there any other commands that will give me the username or person logged in?