Finally, the network is enabled. But now, I'm screwed.
The problem is that Panera's presumably got an all-in-one wireless/router/gateway, as I recall the web page from before it was passing traffic claimed it was a SonicWall, and it's misconfigured. It stopped being visible to me entirely in Monroeville, and at Blvd of the Allies it would be visible but I'd get an error joining or somesuch. But it was available to my wife's Airport Extreme equipped machine. So I deduced that it was 802.11g and was set up to not allow degrading to 802.11b. Annoying.
And getting a Buffalo 802.11g card today did in fact result in me seeing the network (and it uses the Apple Airport Extreme driver, since it has the same Broadcom chipset).
Then I had the problem my wife did. They also appear to have proxy arp turned on on their boxes. That would be great if they were giving routable addresses, and proxy arping on the outside interface. But I'm on the inside interface.
So what this means is if you arp for an address the DHCP server hands out and no one has taken it yet, the DHCP server host itself answers with its own hardware address. The problem is Apple and apparently no one else checks for an in-use IP address by arping the address DHCP gave you, before taking it. Well, crap.
So after some hackery I have a modified IPConfiguration.bundle to try next time. The change? If there's an ARP conflict, it simply ignores it.
There should be some way to set up something in /Library/Preferences to do this. I shouldn't need to hack it.