I'm pretty sure:
new InitialContext().lookup("jdbc/MyDS");
gets the data source from the JNDI context as defined in JBoss in the myDS-ds.xml file.
To get the Spiring data source bean I use:
org.springframework.context.ApplicationContext.getBean("dataSource");
Ultimately I need the Spring configuration because I am defining a whole pile of StoredProcedure beans that need the dataSource as a constructor argument.