Yes, you can use the Terminal Services Manager MMC to see who is connect to the terminal server and log them off if needs be. You can install this by installing the Server 2003 support tools on your machine, or by accessing it on any 2003 Server.
If you find yourself unable to logon to your server via RDP, you can connect using the console, this will connect you to the actual console session, the one you will see if you logged onto the machine using an actual keyboard and monitor to do this, run the following command from the run box:
If using RDP 6 client or above:
mstsc /v ipOfServer /admin
If using older than RDP 6:
mstsc /v ipOfServer /console