apt-get install zabbix-server-pgsql
Get the auto-generated db password out of /etc/zabbix/zabbix_server.conf and use it when prompted in the next step:
apt-get install zabbix-frontend-php
If when you visit localhost/zabbix your browser tries to download a phtml file, you need to:
apt-get install php5-pgsql
and restart apache and the zabbix server.
If you try to import your zabbix config and you get "could not open XML input", you need to increase your "upload_max_filesize" in php.ini.