Thanks for your reply.
After another few hours of messing around, I can name the problem a little more precise:
I can run the tomcat contained in the JBoss-2.4.4_Tomcat-4.0.1-beta package, using the startup.sh. I get the the examples from the webapps directory, and I could also install my old servlets in a new context.
BUT I cannot view the same examples when I start JBoss with the run_with_catalina.sh script.
All I get then is a WebApp: Error 404 (File wa_request.c Line 197).
This is confusing for me: isn't this script supposed to start tomcat too "out of the box", or am I missing some configuration?
I searched this site and all of google to find out how to configure JBoss in conjunction with tomcat. no success.
The system I installed it on: Mac OsX 10.1.
JBoss version: JBoss-2.4.4_Tomcat-4.0.1-beta