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/