A chat program that can be used on a wifi ad-hoc network

Hi team,
I need a chat program that can be used over a wifi ad-hoc network on the machines using windows 7. The ad-hoc network will be created by one laptop and the rest of the 30 machines will connect to it. once connected they should all be able to chat with each other or start a group chat. I checked google and found out that microsoft had an inbuilt software on windows vista called windows meeting space but it was discontinued with windows 7. Any help would be appreciated. Thanks