Do you have a MacOSX server program that runs on your machine? (That is, not a Windows program or a Linux program or ...) If you have such a program, have you tried running it with the example config file provided (copied to the name the instructions indicate but otherwise unchanged)? If you have, what happens?
If you need something that's not there, I'm afraid I can't help other than suggest you either get a Linux server (very cheap but not so easy) or a Windows PC (easier but not so cheap) just for the NINJAM server.