It should only repeat if you ask it to loop the playback (check settings).

Animating a button is just several movies in one.
You make the button on one timeline, then make the animation you want to happen on the mouse over and drop it into the mix (sry, it's actionscript time) and the same for mouse down's, etc, etc.

THIS may help but there are loads more out there.
I haven't used Flash for ages so I had to Google for it.