Auto scrolling listbox

I don’t know if anyone has ever tried this, but I thought that it would be a cool usability thing if, when the user gets to the bottom of a listbox, it scrolls down one or two places automatically. Do you know of any code / place on the web that may shed some light on how to do this? It has proven a rather tough feat.

I greatly appreciate any feedback / ideas you may have.

Thanks,

Sam