This is [http://www.mitwf.org/archive/bos04232002.html MichaelOh's] [http://www.newburyopen.net/ Newbury Open Network] in Boston, as installed at the Trident Bookstore... http://radio.weblogs.com/0104369/stories/2002/06/09/WifiWiki%20AirportWithWirelessBridge_files/tridentcomposite2.jpg
...using a [http://www.3com.com/products/en_US/detail.jsp?tab=features&pathtype=purchase&sku=3CWE820A-US 3Com® EthernetClientBridge] to connect wirelessly to the [http://www.newburyopen.net/ Newbury Open Network]gateway.
This configuration can get its data via the AirPort's built in modem, or via an ethernet cable, or wirelessly.
(pictures not to scale)
[http://www.apple.com/airport/ AppleAirport] http://a772.g.akamai.net/7/772/51/e5da8af4a1d902/www.apple.com/airport/images/index_topimage11092001.jpg
[http://www.3com.com/products/en_US/detail.jsp?tab=features&pathtype=purchase&sku=3CWE820A-US 3Com® EthernetClientBridge] http://www.3com.com/products/prodimage/image/prd_lg_3cwe820a.jpg
Here are Jon Schull's assembly instructions for a wifibox-esque unit http://radio.weblogs.com/0104369/stories/2002/06/09/WifiWiki%20AirportWithWirelessBridge_files/buildawifibucket.gif
-- JonSchull