Here is how to debug orion/oc4j in JBuilder (even with Foundation): http://www.orionsupport.com/articles/jbuilder-debugging.html

In IE to get more information than "500 Internal server error" disable "friendly error messages". This is done under Internet-options -> advanced and will show you the real error message.

Oracle FAQCan I view the Servlet code generated from a JSP after translation?
Yes. To do this, specify the "development=true" attribute in the global-web-application.xml configuration file. The generated servlet code will be saved in the persitstence directory for your application. The persistence directory can be found in the $ORACLE_J2EE_HOME/application-deployments/application directory, where application is the name of the application you are using.

Currently still unsure exactly how to debug jsp.