I wrote up a chapter in the manual, http://www.jboss.org/documentation/HTML/ch03.html, although it is focused on the jboss 3 version, which has some slight differences: bug fixes and better naming. All database access in jboss 3 goes through resource adapters, usually through jca-jdbc wrappers. The jms ra adapter is used quite a bit in the tests and I think in (one of the?) jmx connectors.
What resource adapter are you using? If publicly available, will you contribute a working configuration?