I can confirm that an Australian TiVoHD works in New Zealand!
The in-laws picked up a $498 160Gb unit from JB HiFi for us.

Before opening the box I activated the TiVo on the New Zealand TiVo website (mytivo.co.nz) but I don't know that this makes any difference.

During guided setup no channels were found during the scan, but I expected that was due to the old software not supporting H.264/AAC broadcasts.

Once guided setup was complete, the system information screen showed that the software version was 8.2a01-2-663 and the country was Australia.

It was then necessary to force 3 'daily calls' and reboot untill the software updated to version 11.3b2-01-2-663. It still was not possible to find any channels during a scan.

The trick then is to go to settings>channels>channel list>change area code.
Selecte "No" when asked if the information (Antenna, area code) is correct. You then get prompted as to which country you are in! You then select NZ (obviously) and don't get a choice of area code. You can then sucessfully scan for NZ channels!