Hi kriti,
I think if you want to prepare for the certification
Head First EJB by Bert Bates and Kathy Sierra is a good book to start. If you want to have a more profound knowledge of EJBs you can read
Mastering Enterprise JavaBeans (2nd Edition) by Ed Roman, Scott W. Ambler, Tyler Jewell.
Remember that these books are about the EJB 2.0 specification and maybe at your work place they are still using the EJB 1.1 specification.
[ April 24, 2004: Message edited by: Jeroen van der Velden ]