Buffalo WHR-G54S Supplementary Manual page 5

Under Add New WDS Partner Access Point, enter the wireless MAC address of
the first AirStation (available from the bottom of the first AirStation), with each
pair of digits separated by a colon, e.g. MAC:000D0B10F779 would be entered
00:0D:0B:10:F7:79. Click New Partner when done. The AirStation will reboot, and
when the screen refreshes, the first AirStation's MAC address will be listed under
Bridgeable Access Points.
The two AirStations are now linked by a wireless bridge. Unplug all the network cables and test the bridge by logging
into each of the access points with a wireless client. You should be able to connect to either of the access points from
Windows Wireless Network connection, getting an IP address assigned to your client with no error messages. You should
also be able to log into both of their Web-Based Configuration Utilities by entering their IP addresses into a web browser
(192.168.11.1 for the main access point; 192.168.11.100 for the bridged access point). If the first AirStation is connected
to the internet, you should be able to connect to the second AirStation and surf the web.
Once you can connect to each of your access points, you should configure WEP
encryption. Without WEP, anyone within range of your access points can easily
connect to your network. From within the second AirStation's Web-Based
Configuration Utility (192.168.11.100), click on Advanced, then Wireless Config,
then Security. Note that you must set up WEP on the bridge (second AirStation)
first, before configuring it on the main router (first AirStation), or you will have to
reconnect the network cables to finish configuration.