Note that there is not one single book to prepare you for the exam!
Start your preparation by reading either EJB 3 in Action (Manning) or Enterprise JavaBeans 3.1 (OReilly, 6th Edition).
I have made a summary of the specifications that are important for the certification (check the notes section of the OCEEJBD-Links
). Read, understand and study those and finally get the Enthuware mock exams.
Don't forget to write your own code to verify what you have learned.
Good Luck! ....and don't forget to post your questions in this forum.