Just put your button inside a looping movie clip. This movie clip should have 8 keyframes, each containing an instance of the same button. Now, here's the trick.. All the keyframes will LOOK the same, but you can give each button a different action! The user will have no idea that the button is continually changing.. but each time they click it, chances are they will hit a different button.
Essentially, the trick is to use the user as the random element!
I hope that will work in Flash 3, I think it will.. If you have any questions, let me know!