The configuration of a datasource may look rather complicated when your doing it the first time, therefore you should find a good example and modify it according to your needs.
In $JBOSS_HOME/docs/examples/jca you can find oracle-service.xml. You need to slightly modify it to e.g. assign the JNDI name of your choice to the datasource, enter your ConnectionURL, UserName and Password, then you should be able to deploy it. We're using it for Oracle 9i and it works.
Note that the datasource is always bound under the java: namespace in JNDI.
See also chapter 10 of the Quick Start Guide.
Have a look at:
edit it and drop it into your deploy directory.
Have a look in your JBoss home directory at:
Edit the file and simply drop it into your deploy directory
Simply find and edit docs/examples/jca/oracle-service.xml and drop it into your deploy directory
Check chapter 10 of the Quick Start Guide ("Connecting to databases ...")
In $JBOSS_HOME/docs/examples/jca you can find oracle-service.xml. Slightly adapt with your desired datasource JNDI-name, UserName, Password and ConnectionURL and deploy it. You also find an xa capable *service.xml file, but I didn't try out if it also works.