In Windows (XP+ natively, Windows 2000 with additional software), you can connect to other Windows computers via Remote Desktop Connection (RDC) or Terminal Services Client (TSC). The problem is, if someone is already logged in locally on destination computer, once they give permission for the remote user to take control of their system, the screen blanks out and the local user cannot see what the remote user is doing.
Luckily, you can easily setup a shadow session in Windows 2003 (and not quite so easily in XP), which allows the remote user to control the console session while the local user can still see what’s happening on the local console.
KB278845 details how to shadow a Windows 2003 console session.
Shadowing a Windows XP machine from an XP machine is more difficult and is documented (poorly) in KB279656. Even the Windows XP product documentation is vague and doesn’t really explain the connection process.
Luckily, MSTerminalServices.org has a FAQ that helps to clarify the process of shadowing an XP machine from an XP machine. If you’d like even more information, read Mitch Tulloch’s Windows Server Hack article on shadowing.
Be aware that there is a hotfix available for an issue when you are using Web client computers that are running Microsoft Windows Server 2003 or Microsoft Windows XP, when you run a shadow session between two Web client computers by using Terminal Services, the shadow session is disconnected
Remember, to disconnect the shadow session from the remote side, press CTRL + * (on the numeric keypad), and you will be returned to the original session that you established to the Windows 2003 server.
On a related note, the Friendly How-To Geek has a command line solution for the dreaded error “The terminal server has exceeded the maximum number of allowed connections. The system can not log you on. The system has reached its licensed logon limit. Please try again later.”