And we welcome another NZer to the forums
I'm not quite sure how the Kobo registration process goes, but basically, so long as your device is registered to an Adobe ID, you can read any epub with Adobe DRM. Register an account with Adobe, and download and install Adobe Digital Editions (ADE). Once ADE is installed, run it and authorise your computer to your Adobe account. Once that is done, you can plug in the Kobo reader, and ADE should ask you to authorise it.
Once your Kobo is authorised for ADE, you can buy from any store that supports Adobe epubs. This includes the Kobo store, and the Whitcoulls store.