così va bene ?

codice:
mc.onRollOver=function(){
	this.onEnterFrame=function(){
		if(this._y < 250){this._y +=5}else{delete this.onEnterFrame;}
	}
}

mc.onRollOut=function(){
	this.onEnterFrame=function(){
		if(this._y > 100){this._y -=5}else{delete this.onEnterFrame;}
	}
}