2
Tufat offer a flash chat module, which works ok with smaller sites (ie less users).
http://tufat.com/If this is for a productions environment then consider investing in some real server chat software like:
http://www.chatblazer.com <--- I've used this for 3 years or there abouts, it's cool, it's fast, although I had many teething issues, but Samuel form their tech support helped me a great deal and all is sorted. I made a basic integration of their client to work with XOOPS. They also offer some kinda of DB option so it can work with X too.
Or
http://www.123flashchat.com <---- they offer a XOOPS plugin too to use usernames and pass from your XOOPS database. I tested the demo version the other month and it worked exceptionally well for myself.
There are many other chat server options out there, but these are my two personal favourites, because of support, and because they listen, or at least have listened to me.