you should try using the following line:
Hope that helps,
changing the res-jndi-name to java:/XAOracleDS does not change anything
sorry to hear that.
But I still think the problem is in your configuration files, since it looks like JBoss doesn't find your resource reference and so decides to use its DefaultDS instead.
I recommend looking at your jboss.xml once again. In my installation, the <resource-managers> section is last, behind the <enterprise-beans> section. I'm not quite sure if this really matters, but since it is defined that way in the DTD, I decided to stick with it - and it works!