JBDS includes Hibernate tools. You are using hbm2java with HibernateToolTask to reverse engineer your db schema to entity classes and config/xml files.
There should be a log that display the actions/errors.
Try running the hbm2java directly from cmd line so you can see the errors.
Other option is to create an Ant script that will do the same thing (use hbm2java to revengr your tables).
Section 2.3 of JPA/Hibernate book covers this as well.