onRollover question

How do I make a movieclip ease from A to B while the user’s mouse is over a button and stop (in between A and B) if the user rolls off the button?

Here is an example:


Go to the weddings link in the Flash Website. If your mouse is over the squiggly button on the right, the images scroll until you roll off your mouse.

Cool effect, but I’m having a tough time replicating it.