first off the link to the class documentation on Adobe Livedocs/MouseEvents:

PLAIN TEXT
Actionscript:
  1. //simple way of creating a default Button
  2. package{
  3.    import flash.display.MovieClip;
  4.    import flash.events.MouseEvent;
  5.    public class NavButton extends MovieClip {
  6.       public function NavButton() {
  7.       this.mouseEnabled = true;//to display the hand cursor on Rollover
  8.       this.buttonMode = true;
  9.       this.addEventListener(MouseEvent.ROLL_OVER, dim);
  10.       this.addEventListener(MouseEvent.ROLL_OUT, bright);
  11.       }
  12.       private function  dim ( event:MouseEvent ) : void{
  13.          this.alpha= .75;
  14.       }
  15.       private function bright(event:MouseEvent):void{
  16.          this.alpha = 1;
  17.       }
  18.    }
  19. }