An extra housing fan won't do very much for the Xbox. One of the heatsinks is completely covered by the CD drive. The other one (the taller heat pipe) might get a little bit of benefit. I'd think you should put it over the heat pipe, with the air blowing IN, to complement the existing direction of air flow. And keep the Xbox on its side, not standing on end. The heat pipe will not work as well in the vertical position.