Microsoft NetMeeting allows people to share their desktops over the Internet. It also allows you to chat and video conference. It can be used for VirtualPairProgramming. It seems like a good way to PropagateXp. -- MartijnMeijering
There are other simular tools, you might want to have a look at if you're not running MicrosoftWindows.
See also VirtualNetworkComputing, GnomeMeeting