There are always issues involved when moving from very old versions (Tomcat 1.x) to more recent versions (Tomcat 5.0.28 ships with JBoss 4.0.2). This might be your first stumbling block.
Secondly, if your app is a simple WAR,
you should be able to drop it into the DEPLOY directory without a hitch. If, however, you are taking advantage of the additional
J2EE technologies (JMS, Datasources, JNDI, etc), you might want to look into wrapping your WAR up in an EAR. Our website offers a free download of chapter 3 that discusses exactly how to create an EAR. (
http://www.jbossatwork.com/articles.html)
Good luck with your upgrade.