Simple ajax dynamic update

This is a simple ajax request.? I have a chat script and i have my own custom php code to display all the chatroom names and the amount of users in each of the room. The information of the rooms and how many users are in my msql database which is already made, but i want the roomusers to update dynamically without a whole page refresh each time the roomusers is updated. To see what the chatroom list looks like at the moment visit my site <[login to view URL]> click the link and login as a guest then click an avatar, you will see the chatrooms on the right side of the screen.