Web-based chat (facebook/google talk style)

I want a web based chat similar to the style of facebook and google talk. I want that chat to sit on top of any existing page, so when the user navigates from page to page, that chat boxes remain on the screen untouched. I don't want to use a database for storing and retrieving messages. I don't want to set a specific time interval on when messages are retrieved. I want it so that when User 1 sends a message to User 2, User 2 should see it on his/her screen right away. If no message are being sent, the application should not be periodically checking for new message. I don't want the user to download any components to have this work. I want this coded in classic asp vbscript, javascript, ajax, and any other technology you need to create this.