i wrote this recently it might be helpful if you want to make it dynamic. r1 is the width of the elipse, r2 is the height, tilt is the rotation, and speed is the number of degrees per frame that it moves at...

Code:

onClipEvent(enterFrame) {
offset += speed;
offset %= 360;
_x = x_center + Math.cos(offset * Math.PI / 180) * r1 * Math.cos(tilt * Math.PI / 180) + Math.sin(offset * Math.PI / 180) * r2 * Math.sin(tilt * Math.PI / 180);
_y = y_center - Math.cos(offset * Math.PI / 180) * r1 * Math.sin(tilt * Math.PI / 180) + Math.sin(offset * Math.PI / 180) * r2 * Math.cos(tilt * Math.PI / 180);
}

hope it's useful.