var miListener:Object = new Object();
miListener.onResize = reSize;
function reSize(Void){
new mx.transitions.Tween(centro, "_x", mx.transitions.easing.Back.easeInOut, centro._x, (Stage.width-centro._width)/2, 20, false);
new mx.transitions.Tween(centro, "_y", mx.transitions.easing.Back.easeInOut, centro._y, (Stage.height-centro._height)/2, 20, false);
new mx.transitions.Tween(derecha, "_x", mx.transitions.easing.Back.easeInOut, derecha._x, (Stage.width-derecha._width)/2, 20, false);
new mx.transitions.Tween(derecha, "_y", mx.transitions.easing.Back.easeInOut, derecha._y, (Stage.height-derecha._height)/2, 20, false);
}
Stage.scaleMode = "noScale";
Stage.align = "TL";
Stage.addListener(miListener);
ayuda....