I have an A1392 Airport Xtreme, so what I would like to do is to use it to Join an Existing Wireless Network, then plug my Time Machine into the LAN port of the Xtreme and then plug other gadgets into the LAN ports of the Time Machine. And also still have other gadgets far away ...
Plus the a1264 Express I purchased has only one E-net port. If I had a router w/ a E-net port and the later A1392 Express w/ 2 ports I would presumably be ok. So what I did was use a Mac w/ an Airport built in to configure the a1264 via Ethernet then save the configuration...