To expand on what Brent is saying, configuring your Postgres server to listen to non-local connections varies wildly between versions. On 8.1 on my Debian server, you do it in
/etc/postgresql/8.1/main/postgresql.conf - there is a line that says "listen_addresses = 'localhost'" and you comment that out. I don't remember for sure if that's the only thing. You may also need to configure connections in pg_hba.conf in that directory.
Previous to 8.x, I think you configured the network in pg_hba.conf as well, and it didn't used to be in /etc/postgresql/, but in /var/lib/pgsql or something like that.