It should be a function of the database -- basically, the listener is there to tell it which port to talk to for each individual database that might be running on that system. It's been a few years since I've had to manage an Oracle server, so my memory's a bit foggy.

I did find a guide on 11g with links on how to move some of the ports, however: http://download.oracle.com/docs/cd/B28359_01/install.111/b32002/app_port.htm. You might need to find something similar for the version you're using. I also can't recall of net8 was supposed to solve these issues (I took the course but never used it), but I think it explained what the various steps were for establishing a connection