Planning to create an Instant Chatting website like yahoo messenger, please help

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I can create instant chatting in my webpage but it is for public chat where all people in the room can view the content. but i need a tool which allows user to create accounts and communicate with each other in a private chat session. so is there any tool which is available for direction installation, which allows me to create different rooms like general chat, sports, movies, dating, other, and also allows users to create accounts and chat with each other instantly i have experience creating lot of websites using PHP and MYSQL. I have experience with Joomla Templates too thanks a lot