I'm trying to get build a navigation menu that will slide up/down a page as a user scrolls up/down. I've got a menu based on the Yahoo! User Interface (YUI) library but I can't seem to figure out how to get it to move down as the user scrolls.

Can anyone give me a hand? Maybe just a simple example of getting a <div> with an id to slide down when scrolling ... then I can adapt that to my situation. I'd also love it if it used the YUI (but I'm not too fussy!)