Floating Navigation bar

I’m developing a website using the Twenty Eleven theme and would like to modify the navigation bar so that, upon scrolling past it, it sticks to the top of the browser window. Then, when scrolling back up again, it would remain in its original position. An example of this is the paragraph on the right of this page: http://fiddle.jshell.net/zsJAr/show/light/

Is this kind of thing possible? I’ve tried some stuff with jQuery as suggested here: http://stackoverflow.com/questions/1216114/how-can-i-make-a-div-stick-to-the-top-of-the-screen-once-its-been-scrolled-to

I can’t seem to get it to work. Has anyone actually achieved something like this with WordPress before?