How do I a roll on/roll off animation for this button?

I have a MC thats contains my buttons (nav) called Buttons_MC. In it I have a button called About.

When someone rolls on the About button I want it to play an animation from movieclip Back_MC. And when person takes mouse off the button I want it to play Back_MC but start on frame 26.

thanks guys

Where is the animation is it inside the About button or is it on stage???

think about adding labels to the frame of your animation.

on (rollOver) {
Back_mc.gotoAndPlay("label name here")
}
on (rollOut) {
Back_mc.gotoAndPlay("label name here")
}