OpacityTween.prototype = new Tween();
OpacityTween.prototype.constructor = Tween;
OpacityTween.superclass = Tween.prototype;

function OpacityTween(obj,func,fromOpacity,toOpacity,duration){
	this.targetObject = obj;
	this.init(new Object(),'x',func,fromOpacity,toOpacity,duration);
};
var o = OpacityTween.prototype;
o.targetObject = {};
o.onMotionChanged = function(evt) {
    var v = evt.target._pos;
    var t = this.targetObject;
    t.style['opacity'] = v / 100;
    t.style['-moz-opacity'] = v / 100;
    if (t.filters) t.filters.alpha['opacity'] = v;
};