Starting postmaster with the option -i

I'm using Postgres 7.1.2 and I need to use TCP/IP connections, so I
want to start Postmaster with the option -i.
The Postmaster is starting allone at the startup of the computer, but
it initiates by itself, I can't start it with that option. I have to
stop it and start it again with the option by myself.
Does anyone know how can I start postmaster (at the startup of the
computer) with the option -i?

Thank you,

Raquel