First off you kinda need to figure out where you want to go.
The North Island has Mt Ruapehu. Biggest fields in NZ, but the crappiest snow, and the biggest crowds. The snow is akin to the US' eastcoast stuff. Icy in the morning, slush in the avo.
www.mtruapehu.com
Mt Hutt is the next one, that's one of the more northern fields in the South Island.
http://www.nzski.com/mthutt/
Then you got the Queenstown fields, Coronet Peak and The Remarkables. Queenstown is NZ's ski town, so it's expensive and hard to get accomadtaion.
Then again, if you're coming from GB, our exchange rate is so shit that money won't be a problem.
A bit further north is Wanaka, with Cardrona and Treble Cone. There is also snowfarm and snowpark which hosts the NZ freeride camp...
www.snow.co.nz has info on all those fields
And heres some info for a working visa
http://www.immigration.govt.nz/work/whs/home.html
best to goto somewhere like www.iepnz.co.nz (which is down at the moment...but it usually works), which have working holiday schemes and shit.
What gravity?