Animated button

hello,

I’ve been learning alot about controlling movie clips and animated rollovers. I learned how to call a movieclip on a rollover, but I was curiouse how you make the actual button itself animated? Heres a few examples:

http://www.zenfestival.com/ (the home and contact buttons)
http://www.void.pt/void.php?lng=en (the main navigation on the top)

Thanks for any help you could give.