Here is a nice little chunk of code that I wrote to help you enable the MouseWheel in your Flash AS3 files.

// Import MouseEvent
import flash.events.MouseEvent;

// Create MouseWheel Event
public function handleMouseWheel(event:MouseEvent){
trace(event.delta);
}

// Add MouseWheel Listener
addEventListener(MouseEvent.MOUSE_WHEEL,handleMouseWheel);

This will trace the movement from the MouseWheel and that value can be used in your Flash movie however you would like. Enjoy!