[ОльгаЮрьевна]

Можно так:

mc.onRollOver = function() {
	this.onEnterFrame = function() {
		if (this._xscale>=200) {
			delete this.onEnterFrame;
		} else {
			this._xscale = this._yscale += 10;
		}
	};
};
mc.onRollOut = function() {
	this.onEnterFrame = function() {
		if (this._xscale<=100) {
			delete this.onEnterFrame;
		} else {
			this._xscale = this._yscale -= 10;
		}
	};
};