MovieClip.prototype.distance = function(x1, y1, x2, y2) {
    var distance:Object = new Object();
    distance.distx = x2-x1;
    distance.disty = y2-y1;
    distance.distance = Math.sqrt((distance.distx*distance.distx)+(distance.disty*distance.disty));
    return distance;
};
//Uso:
_root.onMouseDown=function(){
    distancia=this.distance(obj_mc._x, obj_mc._y, _xmouse, _ymouse);
    trace(distancia.distance);
}