So I get back from the other side of the pond, sit down to set up Linux 2.4.21 on eowyn the laptop, and then magically NAT starts working, and now I can get online with elrond the desktop box -- and he's currently downloading the livecd for Gentoo 1.4rc4, and I'm going to do the whole stage-1 installation, so elrond's going to get a workout compiling everything under the sun, from gcc and glibc to X to logjam :)
It's all about the multiple levels of routing and NAT :) elrond is talking (through a hub, so that doesn't really count) to eowyn, who's doing NAT to make elrond's connections look like hers, and then talking to the wireless router downstairs, which is doing NAT once again, and the router talks to the cablemodem, and beyond that, I don't know where the packets go.
... and that's that. And the important thing is, this whole setup is allowing me to download the new gentoo :)