There is no add-in that will give you a chat or forum capability, no. So there's no supported way to do what you want. If you search the forums, I think you'll find that other users have managed to install forum software on their servers. Doing so is potentially risky; such software will want to make changes to your server's web site, and those changes could potentially cause problems with remote access on your server.
For specifics on how to configure any given forum or IM package you should check with their support resources.I'm not on the WHS team, I just post a lot. :)