Sharing internet with Windows over AirPort

My G5 tower is connected to typical home router via ethernet. This gives it flawless internet connectivity.

To give better wireless access to mobile devices that come to that room for a visit in the far corner of the house where the G5 is located, I got a used AirPort Extreme card for the G5 and installed it, making sure to attach the antenna connector and small t-shaped external antenna (provided with original G5) plugged in the back.

When I powered the G5 back on, it immediately saw the AE card and told me to review settings and press Apply. Under Network prefs, under "Location: Automatic", I chose "Show: AirPort." An AirPort ID is shown, along with the default setting below: "By default, join 'Automatic.'" I left all other network settings as they are--I am not trying to use AirPort to connect the G5 to the main wireless router, since it already has ethernet.

I went to the "Sharing" pref and chose the third pane under it, "Internet". I configured it to read: Share your connection from built-in ethernet . . . using (checkbox on) AirPort. I clicked on the AirPort options in this same pane, and typed in a network name: "ABC wi-fi". Channel is Automatic, and--to keep things simple for now--I left encryption off. I pressed OK to close that small dialog, then hit "Start" in the Sharing/Internet pane, which makes its status message change to "Internet sharing on: sharing your built-in ethernet connection." Success! Well, no.

The AirPort icon in the menu bar was a blank quarter-pie. So I clicked on it, and saw the "open internet sharing" option. A panel appeared where I could turn airport on. I did. The grayed-out Network line of the pane then showed the name of the network I had created back in the Sharing dialog: "ABC wi-fi." And the signal level indicator shows full power, all to the right. All set? Nope! When I go to my Windows laptop and find this new network, I see two new options: One, strangely, is the "Computer Name" shown in the Sharing pref panel, and clicking on it to connect doesn't work. The other option is the network I actually named and shared, "ABC wi-fi," but when I attempt to connect to it, Windows (actually Intel PROSet/Wireless Wi-Fi Connection Utility) insists on stepping me through a series of complex security settings, when it would seem that no security should be required since I didn't enable encryption on the AirPort connection.

Giving up on those security settings, I go back to the Sharing control panel and turn sharing off. I hit the AirPort options button and turn encryption on I leave on WEP 40-bit, which requires me to type in a five character string. I do so. I click OK and restart internet sharing. Again, I am given confirmation of "Internet sharing on: sharing your built-in ethernet connection." I try to connect from Windows again, but am not even presented with the complex security options. It just says "Unable to connect," even though it can clearly see the SSID. I try the same a few more times--no luck. I go get an iPod touch and select the new G5-based network--type in the five characters required for WEP 40-bit, and jump right on. Why can't my Windows 7 laptop connect?