It seems to me your servlets/jsps in tomcat can lookup ejbs as if they're are stand alone java clients, i.e. via jndi. Just make sure you configure your jndi.properties file correctly and make it accessible in your web application's classpath.
If I've understood this right:
The JNDI is a service that Jboss runs.
The jndi.properties file is a part of jboss (not standalone tomcat).
How does the servlets/jsps (running on another computer) know where to find this JNDI?
Do you mean that it should be hard-coded in my servlets/jsps? I would imagine that tomcat had some kind of configuration file refering to a specific jndi-service.