I found the following articles very helpful:

The following two files (git-patches) report the modifications I made:

  1. up to installing the PostgreSQL 9.1 JDBC driver
  2. from the previous step and up to configuring and successfully testing a Postgres 9.1 datasource
This is what I had to do to configure HSQLDB 2.2.9 for JBoss AS 7.1: