Capturing the "scroll down" event?

Question

I'm designing a very simple web page (HTML only), the only "feature" I want to implement is to do something when the user scrolls down the page, is there a way to capture that "event" somehow?

Answer 1

Just for completeness, there's another solution using another JS framework (Mootools)

window.addEvent('scroll',function(e) {
    //do stuff
});