Well it depends on the router model. Some routers allow WDS and I have seen some D-Link routers supporting it. As for cable connectivity, just disable DHCP on the slave router and make it a second AP with a different SSID. Should work automatically if you configure your N900 to connect automatically to the available WiFi AP. As per my testing WDS ain't that reliable so I invested in better external omni directional antennas instead and used a single AP.