I have no experience with Postgres, but did you check the phpinfo - file ? There must be a info regarding Postgres - support enabled. Maybe you can post that part.
With Mysql you have to create a user, which is able to connect to mysql. default is root without password (but only from the local machine). maybe its the same with postgres.
Maybe you want to use phpPgAdmin - completely manage your database from the web.
http://www.phpwizard.net/projects/phpPgAdmin/
(I use a similar product for mysql and it works fine.)
Tomorrow I have to install a new Linux server - maybe I have the time to test your config.
Greetings and a nice weekend,
- Thomas