can't connect to postmaster from other machine

Hi everyone,

I'm new to PostgreSQL, i'm using version 7.1.3 on Mac OS X.1.2. It works
perfectly when I connect through localhost but when I try to connect from
other machine on the network i can't. Anyway, the computers can ping each
other, and other applications on the network work well.

I'm running postmaster with this command line:

          postgres$ postmaster -i -D /usr/local/pgsql/data

And psql from the other machine with this:

         postgres$ psql -h 192.168.0.21

after a lot of time (2 or 3 minutes) it shows this message:

psql: PQconnectPoll() -- connect() failed: Operation timed out
         Is the postmaster running (with -i) at '192.168.0.21'
         and accepting connections on TCP/IP port 5432?

Thanks