1 - Make your button! (make something, select it, press F8 (convert to symbol), select "button", the registration doesn't really matters, click it 2 times, and customize it:

UP - normal
OVER - when the mouse its over it
DOWN - when you click it
The HIT doesn't matter.).
2 - select the first frame and press F9 (actions)

3 - put this code in it:

stop();
4 - then create your animation (doesn't really matters being in the same layer or in another one, and it can begin in the layer 1)

5 - then select the button in the first layer, press F9, and put this code:


on (release) {
gotoAndPlay(2);
}
6 - and your button is done!!!
PS: the number in the second code means which frame the animation will jump to when you press the button, so, if you put the number in 45, the animation will roll on to in the layer 45.
(Sorry for the bad english, I'm Brazillian :p)