Cheers guys!
Joel I'd be keen to join you if the date suits - when are you headed down Surrey ways? Heard good things about that place!
I must admit that I haven't actually been mountain biking in Wellington since I was about 15 - I gave up to play other sports. But back then the firebreaks carved into the bush that run along the hills of the Hutt Valley were great fun and accessible without a car (good for me). A challenging climb up the hills, long, rutty and technical trails along the hills till you choose your path back down - mostly 4WD tracks. You've probably found this already, but there's since been development of a park up in Makara about 10kms out of Wellington central city that is pretty much Mecca for wgtn bikers now I hear. More info here!
http://www.makarapeak.org, and more info on a competition worth checking out if you're into it:
http://www.karapoti.co.nz. It's a beast though be warned!
You made a good choice of destination though mate - Wellington is great for it.