As newbie I want to express a big thanks to JavaRanch community which gave me much more support then JBoss or Hibernate websites (actually, I never had a reply from their forums). So, this is my little contribute.
Anyone who is using jboss-4.0.5.GA with Hibernate and MySql 5, could face a warning message ( SQL Warning 1051 SQLState 42S02 ) while is deploying POJO entities mapped between eachother.
You need to update the hibernate3.jar with the last production release.