You can book any row you like in advance with NZ

If you have no joy with UA, feel free to call NZ reservations and get your seats done there! *insert standard disclaimer that these are 'on request only'. We usually say that to cover the 1% chance that the airport needs to reseat deportees/UMs/etc in your seats (or weight and trim issues, although these are even rarer)
Much useful seating info can be found at
http://www.flyertalk.com/forum/Forum7/HTML/000191.html .. enjoy!
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*Any information given in the email is my personal opinion and not the opinion of my employer.