I am using "jboss-3.0.6_tomcat-4.1.18" and had the same problem. Oracle 9i server had occupied port 8080 and JBoss (tomcat in fact) was trying to listen on the same port and could not.
Well, after wondering here and there - changing this .xml file and that .xml file, I finally foud the one that solved my problem:
In the "...\server\default\deploy" directory, I found a file called "tomcat41-service.xml". I updated this file and replaced 8080 with another number - say - 8181, restarted JBoss - IT WORKED!
I am not sure if this is THE right way to configure JBoss to listen on a different port rather than on default (8080), but it worked for me.
If this is not the right way, I'd much appreciate feedback.