You need to make two changes to your postgresql config to allow it to share its data with the world.
As the postgres super user, you need to first edit $PGDATA/postgresql.conf and change the line
#tcpip_socket = false
to look like:
tcpip_socket = true
Then edit $PGDATA/pg_hba.conf and add a line something like this at the end:
host all 192.168.120.1 255.255.255.255 password
The pg_hba.conf file is self documenting, so read it a bit to see if password is what you want, or trust, or md5 or etc...