I can't get PostgreSQL to work on my system.

It took my three days to install and reinstall PostgreSQL.
Now I have no idea.

My Postgres is v6.4.2(download two days ago).
OS is RedHat v5.1 Linux 2.0.34
CPU P133/32MSDRAM

I followed Administrator's Guide told my installed my Postgres.
When I type "postmaster -i",I got the error message:
FATAL: StreamServerPort: bind() failed: errno=98
        Is another postmaster already running on that port?
        If not, remove socket node (/tmp/.s.PGSQL.5432) and retry.
/usr/local/pgsql/bin/postmaster: cannot create UNIX stream port

There is no .s.PGSQL.5432 in the /tmp/.

By the way,why the port must to be set 5432.