You’ve got a PC out there running Windows XP or a 2003 Server. You want to do a remote desktop session to it and mess with a users computer. The “allow users to connect remotely to this computer” is not enabled. You don’t want to get up and go to the users computer. Open regedit, goto file/connect remote registry. Enter the name of the computer you want to enable the remote desktop on. Navigate to the following registry key:
HKLM\System\CCS\Control\Terminal Server\fDenyTSConnection
Change the value data to 0. Wait a minute or two and you should be able to connect to the remote computer.