Beginner: Expanding Mouse Over Rectangle

:stare: Hey, I know how to do general mosueover which cause cause new objects to load, or display a different frame in the timeline. What I wanted to know is how does one get it to do what looks like to be a motion tween when object is rolled over.

www.skive.co.uk <-- this site has its address you can roll over it and it expands very smoothly anyone have any idea how this is done. This is the type of affect I am after just a general guideline on what tools I should be looking at would be greatful. Thanks
In Advanced… :angel: