Zoom in and out effect?

When a user mouses over an object, I want it to zoom in, then when the cursor moves off it I want it to zoom out back to the original smaller size. I tried converting the object to a button, then on the over state load a movie clip of it zooming in, which worked, but when the cursor moved off the object, it jumps back to the original smaller size instead of having a nice transition.

(I’m using Flash CS3 with AS 2.0…and fairly new at it.)

Thanks