Write some Software

I want there to be a shoutbox on the right side of my website. I want the ability to talk to other users on my website in a public setting by default, and then the ability to select a username and then have a private conversation with them. The idea is for there to be a public chatbox on the right side of my website with a list of users online. And then when you click the person's name, a popup occurs just like a Facebook message where you can talk to the person one on one. I want the chatbox to be available on all pages and update in realtime. Here is the link to my website [login to view URL] I want the chatbox to fit in to the theme of my website