Air port and wireless router
How can I use my air port and non-apple wireless router together to extend my wireless network?
AirPort Express 802.11N (2nd generation), Mac OS X (10.7.5)
Establish a permanent wired Ethernet cable connection from one of the LAN <-> ports on the "main" router to the WAN "O" port on the AirPort.
Configure the AirPort to create a wireless network using the same wireless network name, same wireless security settings and same wireless network password as the main router.
Setup the AirPort to operate in Bridge Mode so that it will work correctly on the network.