Is it possible to tap into or monitor a user session from say a root user? Meaning, observing the user's GUI desktop and all? This would be similar to the Windows Assistance Tool.
If I got the right impression, you could install rdesktop and have similar functionality to RDC.
Alternatively, VNC is always a nice option. If you are looking for something more specific functionality, mention it and I'll update this answer.
The best tutorial to configure a monitoring setup w/multiple screens at once is here: http://thetechnologyteacher.wordpress.com/vncthumbnailviewer/