It turned out that I needed to get the 9.04 ubuntu install image, not the 9.10... it's a known problem that this happens when you use the 9.10 install cd to put it on a system installed from an earlier version. I downloaded and burned the 9.04 install, and basically did the exact same thing and it came right up.

Seems kind of dumb... I actually used the 9.10 install cd because I'd done the dist-upgrade to 9.10 several weeks back, but it turns out that's a no-no.