How to make a movie clip get bigger and smaller on rollover?

I know I've done this before, but could you help me?

I'm trying to roll over a movie clip (button), and have it dynamically increase it's scale, with friction.

What is the code for this?

Also, on roll out, I want it to reverse and go back to it's original position.

Thanks so much.

in root
function scale(who, scale){
eval(who)._xscale+=scale
eval(who)._yscale+=scale
}

in the buttons
on(mouseOver){
_root.scale(this._name, 20) //120%
}
on(rollOut){
root.scale(this._name, -20) //returns to 100%
}

This is very basic, could be much better, but take it at starting point

Good luck
Jorge