Animating flash buttons

Hi there!
I have start making a flash page and I would like som nice buttons.

Well what I have planned is something like the buttons on the fontsforflash webpage.

http://www.fontsforflash.com/

I contacted them but, they could not tell me how to do. They just told me that they used a simple mask. but when i try to mask the over state moves to another place.
Please tell me how to do :slight_smile: