you sign a 15 year contract. At the end of that contract depending on your abilities you may be given a contract extentsion that will continue to be extended so long as you remain a contributing member of the service.
As far as being transferred to the British Army, I have NEVER heard of that!!! I would suggest to you that before you imagine applying for special forces, that you at least join the organisation to see if it is what you want to do, or if you are cut out for it.
The questions you are asking are fairly off the wall (with regards transfers), its not suprising that its not on the NZ Army website. I am sure though if you had rung 0800NZArmy your questions could have been answered. Suffice to say though, comments such as.."as our Army's a stinking hole " would indicate that you are probably not putting your best foot forward...I hope this helps