[Blind-sysadmins] Accessible lan messaging client

Hey all. I'm looking for some accessible messaging client which supports comunication thru private network because i need it for comunication inside the company between the employers ... something like direct comunication from computer to computer. One option is to setup something like windows messsenger or skype but as i said, i would like to disable usage of comunication thru internet if possible. I know for one client called winmessenger which allows the user to see all the computers inside private network as well as chat comunication but it didn't show up to accessible so i'm looking for something similar. Any help would be apreciated. Thanks Mario