It's a bit of a hairy subject unfortunetly, as mumtooboys pointed out it all depends who you ask - many people I have spoken to claim this that and the next thing which hasn't always been true and some of which contradicted what the last person told me
As far as I know, seats from Europe with the ECE european standards sticker can be imported and used here. Seats from the US generally can't be, unless previously approved in NZ which are seats generally sold through outlets/distributers etc.
After looking into seats a little more recently we have decided to get a seat sent from Sweden, which will keep DD RFing till she is well past four. It is a Britax Multitech. ATM we have a Cosco Scenera as it has a longer RFing limit than alot of other seats available here and quite frankly it was all we could afford at the time. The Multitech is costing roughly $700NZD - we have just put aside $$ for the last 5mths to pay for it and it will be sent to Italy for our arrival there. The seat fits from 9kg to 25kg RFing. We went through this site
www.carseat.se
There are some very knowledgeable ladies on TNN that I'm sure will be more than happy to answer anymore indepth questions you have.
Edited by Mamma2N