http://omeka.org/ is a great open source CMS for online exhibits that is used quite a bit in the US university sector. It has an AOI-PMH harvester plugin, but it seems DigitalNZ uses a custom API based off Apache Lucene, not OAI-PMH?

It would be great if someone could write an Omeka plugin using the DigitalNZ API library so we could harvest metadata from your database, and present it in Omeka.