Rollover effect

Was wondering if any one new how to create this type of rollover effect in their menu’s I was looking for the “spring effect” is it as simple as a motion tween, i’ve tried it but couldn’t get it to run smooth like theirs, if anyone has an example and willing to share, I would greatly appreciate it.

http://www.easybit.it/flash2005/main.php?language=eng

cheers