Hi Wolfgang
You are by no means restricted to using Unity with Ubuntu. Not
only are there several alternatives (Kubuntu, Xubuntu, etc) which
you can either install from scratch with a CD, or on your existing
system by installing the xubuntu-desktop or kubuntu-desktop
metapackages, but you can also run whatever window manager you
prefer to use. You definitely don't need to change distributions
to change the environment!
That said, if you want to download Debian, I'd just get the iso
from the canonical source:
http://www.debian.org/CD/http-ftp/#stable
There are no NZ debian iso mirrors that I know of, and other than
it perhaps taking a bit longer to download, you aren't really
disadvantaged by getting it from elsewhere.
If you want a Wheezy iso, I think you'll need to get one of the
debian-testing iso images, eg
http://cdimage.debian.org/cdimage/weekly-builds/amd64/iso-cd/