...

I can't run postmaster.

The terms of the problems are:

Distro - RH 7.1
PGSQL - 7.1.3
I've setup the rc.d script with <chkconfig -add> so to have Postgresql
start at system boot and it works fine!
Now, in order to connect to the DB with a Java application, I need to
configure the Postgres server in order to accept TCP/IP connection. The
Programmer's Guide says to supply the -i flag when starting the postmaster,
but, I think, I'm already running the postmaster.
My question is :
    How can I enable the TCP/IP connection with the database already
running?

I've tried with the postmaster -i but I receive the following message:
    Lock file "/var/lib/pgsql/data/postmaster.pid" already exists.
    Is another postmaster (pid 801) running in "/var/lib/pgsql/data"?