Here's a copy of my reply to a similar question raised on another forum. Sorry, but its a bit lengthy!!

I don't know how reliable this information is, but I've got it from the PSS Shipping Info brochure:

1. Customs Duty & GST

First time immigrants taking up permanent residence can import motor vehicles, motorcycles & boats Duty and GST free, provided they can prove they have owned and used the vehicle overseas for at least 12 months prior to their departure date.

2. Concessionary Entry

Your vehicle will be admitted free of duty and GST provided you satisfy customs that you have the intention of taking up permanent residence for the first time and you have personally owned and used it overseas for at least one year before your date of departure to NZ and that the vehicle is for your own personal use in NZ. You will also be required to complete a Deed of Covenant stipulating that if you sell the vehicle within 2 years, you must pay the duty and GST.

Motorcycles

Motorcycles are imported free of duty but are subject to GST which is payable on the full purchase price (less depreciation) PLUS the freight and insurance costs incurred in transporting to NZ.

Depreciation Deductions

Motorcycles owned and used overseas by the importer for:

less than 90 days Nil
Between 3 & 4 months 13%
Between 4 & 6 months 20%
Between 6 & 9 months 27.5%
Between 9 & 12 months 35%
Between 1 & 2 years 50%
Between 2 & 3 years 60%
Between 3 & 4 years 70%
Over 4 years 75%

You can get more information from Land Transport Safety Authority www.ltsa.govt.nz