There are buses that go to all the ski resorts and you can buy season passes to the buses too.
Atomic Shuttles: phone +64 3 322 8883, fax +64 3 349 3868
Southern Link: phone +64 3 358 8355, fax +64 3 358 8585
Intercity Phone: phone +64 3 377 0951, fax +64 3 377 7790
Some people take a bus (and you can get picked up) or you can walk five to ten minutes into town to get the bus. Some people hitch and The Old Gym is very near to the hitching points for all the mountains. Many people drive their own cars up the mountains each day (around 40 minutes to any of the mountains).