Button Effect

I have created a button effect by converting a drawing into a button using the method of simply right-clicking then click the covert to button option clicked OK. Well after the button was on the stage I added a movie clip to both the Up and Over frames. I would like to know if there is a simple (or advanced) way of adding a movie clip or ActionScript to the button when the mouse rolls off. I know there is the action script “on (RollOut) {” but I am not exactly sure how I can use this to display a different movie clip for my button. Thanks.