If yr application is in the same JVM then you don't need descriptors for EJB in web.xml file.
Read this thread, i have just read that.
http://www.jboss.org/modules/bb/index.html?module=bb&op=viewtopic&t= will explain few things for you.
Not sure where to begin here. Well, for starters, EJB's are deployed in JAR files not WAR files. There is a strict format of how that JAR file is laid out. This standard is defined by Sun. Your Cart, CartBean and CartHome classes will all be part of the JAR file along with some XML deployment descriptors. WAR files will contain things like servlets, jsp, property files, web.xml, jboss-web.xml, html, graphics and more. JBOSS will deploy WAR files to the web container and JAR files containing EJB's to its EJB container.
Looks like you are working with the cart example that comes with the j2ee reference implementation. I did that and will upload it for your review.