Hi Carlos,
You can start by looking if pg_hba.conf is really existing or not. I dont have an RPM install of Postgres but I believe it must be in /var/lib/pgsql. You can also try "locate pg_hba.conf" to locate the file.
If the file is not existing and no other files are in /var/lib/pgsql you may have to reinitialize the database via initdb. Or maybe doing a "/etc/rc.d/init.d/postgres restart" may detect that there is no database initialize and it will do it for you. Hope this help, post some more if you need further help.
