James...I use a Java based Chatroom (remotely hosted) called Quickchat, http://www.quickchat.org. It is very flexible, low-cost and the tech support is great. I usually get reply emails within an hour or so.
You can easily change most aspects of the look itself in the applet code you embed into your HTML The free chat has a banner, but the pro version (about $150US) is banner free. It's a very good deal as there is no user limit.