not sure since I don't use tomcat 5, but try looking at tomcat 4 documentation to see how to set up admin tools in tomcat 4 (you need to add tomcat users and stuff). the admin stuff is included in tomcat 4.
For a quick check, try doing something like http://localhost:8080/admin
if you get prompted for username and password, then it's probably working. I still think you need to setup tomcat users though.