Looking for a chat software to run on my site

Hi guys. I would like to run a chat software on my site. Think of one of those old fashioned AOL public chat rooms. The key requirement being that it should integrate with my mysql users tables in order to manage authentication. I had been using this one: http://tufat.com/s_flash_chat_chatroom.htm but its not mature enough for more than 20+ simulatenous users. Anyone have any tips?