Accessing PostgreSQL from a remote host

As a newbie, I would like to know exactly what I have to
do (and how) (on the server) in order to get a running connection to my
PostgreSQL database from a remote host (using a GUI
client).

I'm going to get mad since I've tried everything I could
read about this topic without any success for hours ;-)

MacOS X 10.2.4
PostgreSQL 7.3 (Marc Liyanage package)

Thanks !

Stephane