onClipEvent (enterFrame) {
        var speed:Number = 10;//This can be any number you want.
        this._x += speed;// moves the MovieClip along the x axis. Change the _x to _y to move the MovieClip along the y axis.
        if (_x>=600) {// as long as the registration point for the MovieClip is Greater Than or Equal To 600, the MovieClip will move.
                 this._x= speed/2;
        }
}