i've done a little more work on this, because i'm buying some bridges soon, and buffalo have told me that bridging is only possible with other buffalo bridges...so the WBR-G54 can talk to client cards, but not to non-Buffalo bridges, and the same goes for all bridge functions on D-Link and Netgear bridges, they need to talk to their own make of wireless devices for bridging to work.
So you were right, your friend needs to buy a WBR-G54 or a WLA-G54...as they have WDS.
Or you can get your mate to buy a client PCI/cardbus 54Mbit card...that will connect to your router/bridge.