I've done this one before and it was STUNNING!!! It's an amazing park. Here my blog fom the last trip (sorry in German, but you might get the sense with the pictures) http://neuseeland.jaana.net/#post117
You will need to have decent tramping gear and have all your supplies, hut pass etc. sorted for a 2 days hike. The huts can't be pre booked - so we gotta be quick!
This group is all about hiking and tramping and exploring Wellington Region and further afield. We cover everything from a few hours over day and weekend tramps and welcome experienced trampers to organise and guide. Sometimes we even go for a Sunday afternoon Stroll along the coast - but that's the exception.
If you sign up for a tramp - read carefully, make sure your fitness level matches the description and you do have the appropriate gear. If you are unsure - please get in contact with the organiser of the particular tramp or one of the group organisers. We'd rather you ask lots of questions than something happening!