I'm currently testing the following software packages:
Unreal 3.2 IRC Server
Cygnus IRC Services (Registration of Nicks and Channels)
OperServ (for doing serverwide bans and some stats)
EIRC (Open-Source chat client - java based)
I currently run a normal irc server + irc services. Users can connect via Java-Applet or via mIRC. They can register their Chatnicks so that nobody else can use them. Unfortunately, the db of the chat and ubb.Threads can't exchange any data.
Cygnus Services offer a webfrontend (php) to read and write data to the chatserver db.
It should be possible to modify the forum adduser script, to register the username on the irc-server aswell.
It should also be possible to modify the Java-Applet so that the users are logged in with their forum-username.