This week's book giveaway is in the OCPJP forum. We're giving away four copies of OCA/OCP Java SE 7 Programmer I & II Study Guide and have Kathy Sierra & Bert Bates on-line! See this thread for details.
Have you checked out EJB by OReily. I believe they have a chapter that talks about the EJB 2 and 3 beans interoperability. That might help you.
I have one doubt though, when you migrate your entity beans to JPA entities, would you be modifying the existing code base? If yes then why not take annotations?