install packages

apt-get install git-core

checkout source

cd /srv
git clone git://git.koha.org/pub/scm/koha.git koha

and follow /srv/koha/INSTALL.debian which is more correct than other instruction on web.

./vz-create.pl --dist=lenny koha.ffzg.hr

Here is some specific tuning to make Koha work with PostgreSQL:

sudo -u postgres createdb --owner=kohaadmin --encoding=utf-8 koha
sudo -u postgres createlang plpgsql koha

client_min_messages = error

local   all         all                               trust
host    all         all         127.0.0.1/32          trust