MDBs stand for Message Driven Beans.
For learning EJBs I recommend Ed Roman's "Mastering Enterprise Java Beans 2nd edition" and Floyd Marinescu's "EJB Design Patterns".
About Jakarta Struts you can read at jakarta.apache.org/struts/
Also you can read and post your questions here on javaranch on the forums dedicated to JSP/Servlets/Struts...
It's all on the net
[ January 13, 2004: Message edited by: sergiu truta ]