Is there a program that can IM to nodes on a p2p network for windows 7

I am operating a p2p network of 5-6 machines all running windows 7 and would like to have the ability to send messages to operators in their suites.

Preferably something built in to the OS if possible and if not, then as lightweight and basic as possible. I guess I was looking for a winchat replacement. I did find a third party program called LanMSGR which seemed like it'd be pretty good but it required that the .net framework be installed. While that likely shouldn't matter, I'm using the machine and the others in the network in a post production environment running Avid Media Composer software on all machines.

This software can be quite temperamental about the environment it operates in and the fewer additions to windows and third party software applications I install the better because it makes it easier to diagnose issues as they arise if there are less variables at play.