You need to ensure two things:
<p>
  <i>1)</i> You need to configure your PostgreSQL server to allow TCP/IP
  connections. You can do this by setting the "tcpip_socket" variable
     to "true" in the postgresql.conf file (usually located in ~postgres/data).
     <br />
     Some older PostgreSQL daemons (prior 7.0) need to be started with the
     "-i" commandline option.
</p>
<p>
  <i>2)</i> You need to patch your <tt>pg_hba.conf</tt> to allow TCP/IP host
  connections.<br />
  Example (for PostgreSQL 7.3):
</p>
<pre>
local   all         all                                            trust
host    all         all         127.0.0.1         255.255.255.0    trust
host    all         all         0.0.0.0           255.255.255.255  reject
</pre>
<p>
  Example (for PostgreSQL 7.2):
</p>
<pre>
local           all                                            trust
host            all         127.0.0.1         255.255.255.0    trust
host            all         0.0.0.0           255.255.255.255  reject
</pre>

<p>
  To get a secure setup, replace <tt>trust</tt> with <tt>password</tt>,
  <tt>md5</tt> or something else (depends on your PostgreSQL version).
</p>
<p>
  Don't forget to restart PostgreSQL after applying the changes!
  (e.g. <tt>/etc/init.d/postgresql restart</tt>)
</p>