One nice thing about Java is the same .class files should run the same on all operating systems, so you won't have to modify anything to make it run on Linux as opposed to, say, Windows. However, for you to actually use the chat client with your friends, there will have to be a chat server accessible across a network, and all your friends will have to run the same client, or at least a client compatible with that server. I don't have the HeadFirst book, so I don't know the specifics of the chat client you refer to, but they must mention a server, right?
Also, your server will have to have the ports listened to by the chat server open, which is unlikely in an "enterprise" environment like a college. Is there an administrator you can speak with to make sure?
Have you tried? If so, what happened?