I am running RedHat 7.3 with PostgreSQL 7.2.1. I downloaded the drupal 4.0.0.tgz file and installed it under my docoot (http://my.site.com/drupal/).
I ran the database.pgsql install script, wich worked fine (after changing the username from 'root' to 'postgres'.
I then went to http://my.site.com/drupal. There were two links: Home and User Account. I clicked on 'User Account', filled out the creation form, and pressed submit.