Risolto!! solita svista!! vi allego quello giusto...
codice:
onClipEvent (load) {
	import mx.transitions.Tween;
	import mx.transitions.easing.Elastic;

	var N_TW:Tween = new Tween(_root.N_MC, "_y", Elastic.easeOut, 120, 90, 30, false);
	var tweenListener:Object = new Object();
	tweenListener.onMotionFinished = function() {
		_root.nextFrame();
	};
	N_TW.addListener(tweenListener);
}
Grazie a tutti!!!!