There are a lot of guides on the net on how to configure and set this all up. I think your best bet would be to hit one of the private server sites and read through their FAQs and then apply that to your setup.
I must be living in the dark ages, I didn't know L2 had a Mac Client. How does it run and what kind of mac do you have? Where did you find the server, is this something I can get off a torrent?