Unless I am wrong, I think there is no "example" or "test" application that ships with the JBoss 3.0 binaries. You will have to create a sample app and deploy it to see if it is working.
However, you can try bringing up the JMX Console. If you have the JBoss 3.0.0 release, try:
If you have the 3.0.1 alpha or the head version from sourceforge, try: