flash scroll mousewheel help

I have 2 movie clips, one called content, the other called scroller which move up and down when the mouse wheel is scrolled. (one goes up while the other goes down)

The problem I'm trying to figure out now is how to stop the scrolling when they reach the boundaries of the page.

AS:

mouseListener = new Object();

mouseListener.onMouseWheel = function (delta) {
// This works, but it doesn't stop at the edges
content._y += delta;
scroller._y -= delta;
}


Mouse.addListener(mouseListener);


from the tutorial Here

I'm still mostly just learning this stuff at this point, so the dumber the instructions/tips, the better. Thanks!