How can I log in and authenticate to PostgreSQL after a fresh install?

I did a new install of PostgreSQL 8.4 on [Linux Mint][1]/[Ubuntu][2]. How do I create a user for PostgreSQL and log in using *psql*? When I type `psql`, it just tells me > psql: FATAL: Ident authentication failed for user "my-ubuntu-username" [1]: https://en.wikipedia.org/wiki/Linux_Mint [2]: https://en.wikipedia.org/wiki/Ubuntu_%28operating_system%29