W2K3 TS Stop another W/Stn logging in as a logged in user

W2k3 Server Std running TS
If a user is already logged in as say, Sysadmin (has all admin rights) is there a way to stop someone else logging in from another W/stn as Sysadmin and then bumping off the first logged in Sysadmin ?
Many Thanks for any help.

Regards
TerryF