function pressedMyPianoKey(){
   // Do something like pianoKey.gotoAndStop(2) to show a new graphic
}

stage.addEventListener(KeyboardEvent.KEY_DOWN, keyDown);
function keyDown(event:KeyboardEvent):void
{
    pressedMyPianoKey();
}

pianoKey.addEventListener(MouseEvent.CLICK, click);
function click(e:MouseEvent){
    pressedMyPianoKey();
}