I installed Postgres8 on Ubuntu (http://docs.moodle.org/en/Installing_Postgres_for_PHP)
Then I checked out a fresh Moodle 19 Stable
During the Moodle installation process, on the database page I had to enter into the HOST field:
host='localhost' port=5432 dbname='moodle' user='moodleuser' password='password'
If I tried to use the other fields (use,password,database) that I would expect to be used, I had a message: 'Can not connect to the database'.
I guess it could be a problem of the missing port field...
We could either fix it, either add some more information on this page in order to help the administrator.