VNC

http://www.tightvnc.com/

VNC lets one control their computer remotely as if they were
sitting in front of it. You see what's on the screen and can
operate the computer the same way. Sure WinXP has remote
assistance but it's not the same thing. In WinXP home Ican
request assistance but cannot control another machine with it.

VNC is also cross platform, meaning you can run the server on a
windows machine and control it from a Linux box, or vice versa.

Everyone should have VNC installed on their computer, that way
if you're having computer problems, instead of trying to tell
your friendly computer geek friend what you see on your screen,
she can actually see the screen and directly help you fix your
problem.

--
Makeup, it takes believing in. Like a magic carpet, it's belief
that makes it fly. Otherwise, it's just a rug.
If you believe in it, makeup has a magic all it's own.
Of course, makeup is only dime-store magic. But it works well
enough, when it's used properly.", the makeup artist, from the
book Sooner or Later, based on the 1978 TV movie of the same
name.