Welcome. If you don't have dumps (just the files managed by postgres), then you're going to want to start the same postgres version that was used when the site was running in 2003, and make a textual database dump.
Whenever I back up, I keep two things: (1) the complete set of files that is the service (incl. the aolserver config file and if applicable the "run" file that daemontools uses, and (2) the database dump file.
