to make it short, you can not apply what is working with a standalone tomcat + struts project to a jboss one.
JBoss manages Tomcat through a service. Just have a look at your deploy directory and the jbossweb-tomcat-5.0.sar subdirectory.
See chapter 9 of the JBoss 4.0 documentation for a more detailed explanation of the JBoss/Tomcat 5 integration bundle.
After that, no difficulty should occur if your .war file is correctly build. Please detail what kind of problem do you encounter if you want people to help you efficiently.