I have set up a new JBoss 7.0.1 server and make the changes like you and it works... It seems, that the problem is Jboss 6.
I think I have to upgrade at JBoss 7. Your post about Hibernate 3 on Jboss 7 are very usefull now
But can you test it on Jboss 6? I don't know if the migration to Jboss 7 works.