This week's book giveaways are in the Refactoring and Agile forums. We're giving away four copies each of Re-engineering Legacy Software and Docker in Action and have the authors on-line! See this thread and this one for details.
They are tomcat/shared/lib and tomcat/shared/classes.
The hierarchy was simplified in version 6. I believe it's now just tomcat/lib
Be sure to read the release notes carefully. There is a section in there on JNI resources shared by multiple apps with some specific information on initializing them to insure that one app doesn't lock the others out.