Prova questo (è di ahab). Associ al movieclip:

codice:
onClipEvent (load) {
	speed = 1;
	x = -100;
	a = -.005;
	p = -100;
	q = 100;
	xctr = 275;
	yctr = 200;
}
onClipEvent (enterFrame) {
	if (x < 100) {
		y = a * (x - p) * (x - q);
		this._x = xctr + x;
		this._y = yctr - y;
		x = x + 20;
	}
}