Sounds to me like you need to look into the Tomcat docs. Tomcat is the underlying 'web server' and pretty much provides all your requested features.
Depending on what you want to do, standalone Tomcat or Resin might be good enough.
Reconfigure port 80: look into $JBOSS_HOME/server/your-server/deploy/jbosswb-tomcat*.sar/server.xml, there you'll find the list of connectors (for JBoss 4.x).
It might also be a good idea to do port forwards on your firewall so that HTTP requests to port 80 are transferred to another host/port combination.