Authentication problems are usually a result of not having the settings in your pg_hba.conf file set just right. For a test/demo deploy, the easiest way to get it working is to set postgres to just "trust" any IP connection on 127.0.0.1 for the "postgres" user. Neddick defaults to using the postgres user (but you can change that if you want), and then you just have to add the argument
-U postgres
on the command line when you run the sql scripts using the psql command.
If you want to make the postgres connection secure, you'll need to enable real authentication in postgres. That should all be documented in the postgres docs, but if you have trouble making it work, let us know and we'll see if we can help you get it sorted.
Phil