Older UK tv's will not work over there. Best to keep them for using as a DVD/video/games screen. However I just got a Sanyo from Tesco and it has the NZ tv standard on the system, so yes some will work dual standard!
The reason the older ones will not work is down to the audio (sound sub-carrier frequency) being a different spacing from the video signal in the two systems. A retune of the system is a specialist job and probably not worth bothering with.
Steve