Just before I gave up entirely and reinstalled, I thought I’d try deleting the config for the wired networking from YaST, and now wireless works correctly again. Woo!
I think for some reason everything networky was being passed to the first interface, i.e. wired, rather than the working interface. The wireless card was getting an IP address, and I could ping the router, but for some reason it was getting no further. There’s probably an explanation and a workaround, but at the moment I don’t really care. If it works, great.
Still waiting for my GP2X… 
And, incidentally, my Logitech G15, which has been on order for a month. Gah.
