Moving back to original position

hi, i was wondering how to do the animation for the navigation in www.fontsforflash.com
when i click on any button, it wud move forward, then, when i click on another random button, the first button would move back to its original position, like in a tweening way…?
i noe it has something to do with the moveBack fuction, but im not good with AS…help pls
thanx in advance :hr: