random directions

[RampnRail]

i was making a quick thing where you could use the arrow keys to drive a car around in an arena and wanted to add in other cars that moved around randomly which you could crash into.
i managed to program the player car,

code:

---

onClipEvent (enterFrame) {

	if (Key.isDown(Key.UP)) {

		speed += 2;

	} else {

		if (Key.isDown(Key.DOWN)) {

			speed -= 1;

		} else {

			speed *= .9;

		}

	}

	if (Math.abs(speed)>25) {

		speed *= .6;

	}

	if (Key.isDown(Key.LEFT)) {

		_rotation -= speed;

	}

	if (Key.isDown(Key.RIGHT)) {

		_rotation += speed;

	}

	speed *= .9;

	x = Math.sin(_rotation*(Math.PI/180))*speed;

	y = Math.cos(_rotation*(Math.PI/180))*speed*-1;

	if (!_root.land.hitTest(_x+x, _y+y, true)) {

		_x += x;

		_y += y;

	} else {

		speed *= -.5;

	}

}

---

but i cant program the computer car to move randomly based upon the same physics.
working with flash 5, please help