Hello, 
 Is it possible to configure JBoss/Hibernate so that hibernate can
lookup the mapping files from another jar (e.g. myHibernateClasses.jar)

Example:
myEar.ear
 hibernateStartup.sar
   META-INF/
            jboss-service.xml

 myHibernateClasses.jar
   eg/
      package/
             MyClass.class
             MyClass.hbm.xml


This configuration would allow to deploy the EAR in exploded format.