Install on Debian etch
Following along instruction about Installing on Debian  and taking git checkout bits 

Contents: [Dobrica Pavlinušić's random unstructured stuff]
• Dobrica Pavlinušić's random unstructured stuff (install packages) 
• Dobrica Pavlinušić's random unstructured stuff (checkout source) 
• Dobrica Pavlinušić's random unstructured stuff (koha.ffzg.hr) 
• Dobrica Pavlinušić's random unstructured stuff (PostgreSQL) 
• Dobrica Pavlinušić's random unstructured stuff (Create database) 
• Dobrica Pavlinušić's random unstructured stuff (/etc/postgresql/8.3/main/postgresql.conf) 
• Dobrica Pavlinušić's random unstructured stuff (/etc/postgresql/8.3/main/pg_hba.conf) 

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

PostgreSQL
Here is some specific tuning to make Koha work with PostgreSQL:
Create database
sudo -u postgres createdb --owner=kohaadmin --encoding=utf-8 koha
sudo -u postgres createlang plpgsql koha

/etc/postgresql/8.3/main/postgresql.conf
client_min_messages = error

/etc/postgresql/8.3/main/pg_hba.conf
local   all         all                               trust
host    all         all         127.0.0.1/32          trust