Ok, I've tried those suggestions:

I ran palmod_config and selected the NZ frequency table. Before this, I was (probably coincidentally) getting one channel - TV2. After, I am getting no channels. So I don't think I am doing anything wrong - I think the Christchurch postcode has been fully implemented in ozTivo 1.6.2 (which is confirmed by below).

I edited /etc/postcodezones and added Christchurch (02123). /bin/ntpdate ... does not have the error now, but it does say "Failed to connect to any of the time servers". I guess it doesn't work with a modem. Back in tivo, time is still wrong. I didn't wait for a daily update (because is not modem not connecting now), but I suspect that is would have change the time then). So I think this is fixed (someone may want to add the Christchurch postcode to the next ozTivo image release).

I double-checked the modem settings, and it seems like it should work, but it doesn't. I even put the tivo hdd back in my pc and re-did the settings through knoppix (setting the emulator doesn't crash there). However, when I looked at the changes it made, they were the same as nic_config_tivo - even the emulator adrress had been changed to 127.0.0.1 in tclient.conf. Maybe the address doesn't matter there, because the correct nz emulator IP is in oztivo.conf. Anyway, I even tried a second ISP, but had the same problem. As my modem worked before nic_config_tivo, I think this is a problem with nic_config_tivo - maybe when it failed, or maybe when changing from turbonet to modem, there is something it forgets to change. But I guess as modem is not supported, maybe I can't hope for too much.

And then I used nic_config_tivo to setup TurboNet use instead of modem. I could telnet in over lan, establish an ftp connection on ftp://tivo'siIP, but going to TivoWebPlus at http://tivo'siIP did not work. After less than 30 minutes usgin LAN, my tivo started crashing - remote did not work, telnet connection stopped responding and the subtle moving graphics in the background stopped moving. After a hard reset it worked for a few minutes and then crashed again. After another hard reset it only lasted for about 10 seconds. I'm guessing that is a problem with my turbonet card rather than the ozTivo image.