That shouldn't be too hard to recreate. You could even do it on the timeline if you really wanted.
Personally, I would to it with TweenLite.
You just have to scale it in from the left with a fade on rollover and then scale it out to the right with a fade on rollout. There is no "flipping" happening, it just looks kind of like it.
One thing I noticed about that site, is that the mouse over hit area is smaller then the image being "flipped." That can be done by either assigning a hitarea or just have the animation happen in the background while the alpha=0 buttons are in front.
"Give a man a fish and you feed him for a day. Teach a man to fish and you feed him for a lifetime." -- Chinese Proverb.