Mark
There is a file called MSCTSC.exe in the client loadpoint of Terminal Services that you can modify. You can disable the cross in te upper corner of the window or the message to stop users disconnecting. You will some form of editing program to do this. Search in a search engine on how to modify this file.
Also you can change the config in user manager so that when a user logs on and there session is idle for a period of time the session will disconnect. Furthermore if the disconnected session is disconnected for longer than 5 minutes it will reset.
Hope this helps!
Neil
Neil Lewis
IT R&D Manager
Velmore Ltd