Managing JBoss Datasources
The JBoss Application Server manages its datasources from inside the $JBOSS/server/<profilename>/deploy directory.
Each datasource is defined as a XML-file named "<somename>Db-ds.xml", for our example pentahoDb-ds.xml
The content of the XML-File looks like that
Oracle Style
<?xml version="1.0" encoding="UTF-8"?>
 <datasources>
  <local-tx-datasource>
   <jndi-name>jdbc/PentahoDS</jndi-name>
   <connection-url>jdbc:oracle:thin:@<HOSTNAME>:<PORT>:<SID></connection-url>
   <driver-class>oracle.jdbc.driver.OracleDriver</driver-class>
   <user-name><USERNAME></user-name>
   <password><PASSWORD></password>
   <max-pool-size>100</max-pool-size>
   <new-connection-sql>select * from DUAL</new-connection-sql>
   <blocking-timeout-millis>200000</blocking-timeout-millis>
       <metadata>
         <type-mapping>Oracle9i</type-mapping>
      </metadata>
  </local-tx-datasource>
 </datasources>
MS SQL Style (using the supplied Microsoft JDBC driver)
<?xml version="1.0" encoding="UTF-8"?>
 <datasources>
  <local-tx-datasource>
   <jndi-name>jdbc/PentahoDS</jndi-name>
   <connection-url>jdbc:sqlserver://<HOSTNAME>:<PORT>;SelectMethod=cursor;databaseName=<DBNAME></connection-url>
   <driver-class>com.microsoft.sqlserver.jdbc.SQLServerDriver</driver-class>
   <user-name><USERNAME></user-name>
   <password><PASSWORD></password>
   <max-pool-size>100</max-pool-size>
   <new-connection-sql>select 1</new-connection-sql>
  </local-tx-datasource>
 </datasources>
MySQL Style (using the MySQL JDBC driver)
<?xml version="1.0" encoding="UTF-8"?>
 <datasources>
  <local-tx-datasource>
   <jndi-name>jdbc/PentahoDS</jndi-name>
   <connection-url>jdbc:mysql://<HOSTNAME>/<DBNAME></connection-url>
   <driver-class>com.mysql.jdbc.Driver</driver-class>
   <user-name><USERNAME></user-name>
   <password><PASSWORD></password>
   <max-pool-size>100</max-pool-size>
  </local-tx-datasource>
 </datasources>
As soon as this is done, you can use the datasource from e.g. pentaho.war/META-INF/context.xml which would then be changed to:
<?xml version="1.0" encoding="UTF-8"?>
<Context path="/pentaho" docbase="webapps/pentaho/">
   <ResourceLink name="jdbc/Hibernate" global="java:jdbc/PentahoDS" type="javax.sql.DataSource" />
 <ResourceLink name="jdbc/Quartz" global="java:jdbc/PentahoDS" type="javax.sql.DataSource" />
</Context>
See that "jdbc/PentahoDS" matches the "jndi-name" defined inside the Datasource-XML.
For details, have a look at the JBoss reference: http://docs.jboss.org/jbossas/docs/Administration_And_Configuration_Guide/5/html/Configuring_JDBC_DataSources.html