[dimarik]

как-то так можно

import mx.transitions.Tween;
import mx.transition.easing.Regular;
 
var app:		MovieClip = this;
var Windoww:		MovieClip;
 
function onLoadInit(target:MovieClip):Void {
	target.mcl.removeListener(this);
	delete target.mcl;
	this.tweenMe(target);
}
 
function tweenMe(target:MovieClip):Void {
	target.varTween = new Tween(target, "_alpha", Regular.easeIn, 0, 100, 1, true);
}
 
// Ваш button - instance name
this.button.onRelease = function():Void {
	if (!app.Windoww.mediaContent) {
		var mcl:MovieClipLoader = new MovieClipLoader();
		var target:MovieClip = app.Windoww.createEmptyMovieClip( 'mediaContent', app.Windoww.getNextHighestDepth() );
		target.mcl = mcl;
		mcl.addListener(app);
		mcl.loadClip(_root.ImgURL, target);
	}
	else app.tweenMe(app.Windoww.mediaContent);
}