Networks

if its a domain environment, you can install a local admin pack, and I think there is Terminal services manager. Right click the domain, connect to computer, throw the IP address in or server name. and it will show all the connections.

Or you can click "Start" right click "my computer" click "manage" right click "computer management, and connect to computer that way and it should show who's connected.

from the Sysinternals suite, free download from MS

http://technet.microsoft.com/en-us/sysinternals/0e18b180-9b7a-4c49-8120-c47c5a693683.aspx