The Apple AirPort base stations CANNOT extend the wireless range of non-Apple wireless routers. That is because they use a propriety method to do so with other AirPort base stations.
However, the AirPort Extreme base station can "extend" other non-Apple wireless routers if the connection between them is wired.
On the other hand, the AirPort Express base station can "join" an existing non-Apple Wi-Fi network as a wireless bridge to share a USB printer.