Creating a popup panel

We are implementing the chat feature in our portal and are using some customizations. We want to have a link at the top of our home page that says "Chit Chat" and when clicked, we want to pop up a window at the bottom of the page the lists all the most recent chats.

How would I accomplish the pop up window which would basically appear on a mouse over event. The form will basically be a repeater, but I am not sure how to make it function as a popup window.

Any help would be appreciated.