In Fedora 7+, postgres is insatlled by default. Its just about a few commands to get started. First of all you have to change the password for the postgres user, postgres. I am pasting the commands below:
#passwd postgres
#chown postgres /var/lib/pgsql/data/
#su - postgres
~initdb -D /var/lib/pgsql/data/
#/etc/rc.d/init.d/postgresql start
You can also install pgadmin3, which is a nice GUI for postgres:
#yum install pgadmin3
If you do not have the repository, you can add it from here:
http://yum.pgsqlrpms.org/reporpms/repoview/letter_p.group.html
I was inspired by this blog:
http://www.postgresonline.com/journal/index.php?/archives/45-An-Almost-Idiots-Guide-to-PostgreSQL-YUM.html