Regarding to your other questions: no need to worry about these issues. The best to learn and get a grasp on things is, create a small sample application (something like this one or just use the one from the tutorial). And if you see something about securitymanager, just delete it (because it is not needed and for the assignment not allowed).
I think you should write your own tutorials. Finally I managed to get a quick and dirty RMI example working and, more importantly, running on two different machines!
Would you (or anyone at all of course) mind having a look over this simple example and see if I'm doing the right thing. It's not part of my SCJD;
1. Place the above code in a directory called "hello".
2. Built with javac hello/*.java
3. Create the stub with rmic hello.Server
4. Create a Jar file as follows;
jar cvfe runme.jar hello.RunMe hello/*.class
1. Move the runme.jar to some directory far away from "hello" (to ensure its not using the classes in the classpath).
2. Run the server with;
java -jar runme.jar Server <port> <serviceName>
e.g. java -jar runme.jar Server 2000 JohnService
3. Run the client with;
java -jar runme.jar Client <host> <port> <serviceName>
e.g. java -jar runme.jar Client localhost 2000 JohnService
You could even run the Server on another machine, so long as it is accessible from the one you run the client on and specify its hostname on the cmd line.