Six gigs later I find that 32bit ubuntu has no himem support and have to upgrade.
I run the antique nvidia-173 driver because one of the two video cards is a 5200. My problem after install was a string of errors (EE) No devices detected errors which, as it does, drove me to xorg.conf. What I realised was that the nvidia-settings thingy had left out the Bus IDs for the cards inserting instead lines like BusID “?@?:?:?”.
lspci to the rescue, and after I inserted the proper IDs (make sure to replace the XX:XX.X format returned by lspci with the XX:XX:X format needed by X), everything’s fine.
Just some keywords in case someone else runs into the same thing. And it made today’s XKCD that much more enjoyable, finding it as I did after everything was fixed. I think he has the slope inverted, because I definitely felt pretty good immediately after I got it working. It’s all downhill from here: every moment brings me closer to the next time I’ll have to muck about with it.