General help

I'm running Moodle 1.3.1, on a RedHat 7.3 machine, apache, PHP and postgreSQL, and I'm having troubles setting up the external DB authentication; in a few words, Moodle doesn't find the server (which it's the same that runs moodle's DB). What can be wrong with that feature? Is there anything that I must verify? I'm not very skilled with postgreSQL, so I might have done something wrong...

thanks in advance.  AOL7.3