I’ve been trying out chat applications that work on my home network for a couple of years now. This one is the best I’ve found so far. It has tons of features and it even has a battleship game you can play over a network. I also had fun grabbing remote screenshots from my wife’s PC while she was chatting with me. The ability to run programs on her PC and view files there is a bit more than I need for a chat application, but it might be great for a tech support person.

Quote from the website
Windows Communicator – universal chat client,based on ICQ and IRC functionality and solutions. Application can work on Local Area Networks as well as over the Internet.
Basic application functions:
- sending public messages
- private chat
- private message
- secure channels
- remote screenshot
- remote execution
- list running application
- remote shutdown/reboot/logoff/wake up
- others
Note : Each of listed above spy functions may be blocked by users.
Windows Communicator home page
http://www.communicator.pl/