As everyone above me has mentioned, Australian passport holders are not stamped when entering NZ, as they are automatically granted permanent residence. This is unless you have done something in the past which the NZ deems you a security risk, meaning you will have to apply for a NZ visa and will get a stamp upon arrival.

NZ permanent residents (the non-Aussie type) have their residence permit in the form of a sticker in their passport. IIRC when they first enter the country, the visa is stamped with a date, and no stamp is given after that.