I don't believe that there are any differences and if there are, there may be a few semantic differences. The easiest thing to do is to copy the context from your Tomcat 4 server.xml into the server.xml for your Tomcat 5 (may a backup copy of the virgin server.xml just in case).
Here is the link to the Tomcat documentation on JNDI for Tomcat 5.5:
http://tomcat.apache.org/tomcat-5.5-doc/jndi-resources-howto.htmlHope this helps!