Ok, I'm going to answer my own question for the benefit of others:
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Here are the steps that I used to successfully configure the WET11 to allow my Blue&White G3 to connect to my existing Airport network:
1. First I connected the computer by hardwire to my DSL router in order to access the network. I use fixed IP addresses rather than DHCP.
2. I downloaded and installed the latest version of Airport software (2.2.1), and used the Airport Admin utility to install the latest update onto the (Graphite) Airport (3.84).
3. I then followed the instructions in AppleCare Document 58613 to reset and initialize the Airport, name the Airport, and set the Airport to an IP address on my Subnet (it connects to an Asante Router which is connected to my DSL modem). I also activated WEP (40-bit) and set a password, which tells you what your WEP key is (a hexadecimal value - write it down).
4. I then connected the computer directly to the WET11, reset it using the reset button, set the computer's IP address to 192.168.1.1, subnet 255.255.255.0, and blank gateway address, and entered the default WET11 address into a web browser:
http://192.168.1.225. This allowed me to log into the WET11 configuration page using "linksys'" username and "admin" as password.
5. I used the WET11 configuration "IP Addr" page to change the device's address to one on my subnet (192.168.123.225) and the ip gateway to my Router address, clicked apply, and rebooted it (on the Admin page), then set my computer IP address back to normal (192.168.123.1) and entered the new ip address of the WET11 into the browser.
6. I then entered the name of my Airport as the SSID on the "Wireless" page, enabled 64-bit WEP, and entered my hexadecimal WEP key into WEP key 1, clicked "apply", and rebooted again.
7. I then set the gateway address of my router on my computer, and entered
www.apple.com in the browser, and was online wirelessly!
8. My conclusion is that my Airport needed the updated software to be compatible with the WET11, which may not be an issue with newer Airports. Also, fiddling with the IP addresses is needed in order to get both devices on the same subnet (i.e. 192.168.*.* or whatever).
9. Finally, the WET11 web configuration only seemed to work if I clicked the APPLY button, then the REBOOT button. If I applied changes to more than one page before rebooting, some changes were not applied.
If anyone has specific questions please feel free to contact me at
wizwoz@mac.com.