First, email
hub_invite@hotmail.com to request a registration. The hub is private to people that have been seen around here - just some friends trading some rare files.
Second, try a more Mac-friendly client. Shakespeer seems to be working well for many of us. Try googling and downloading that instead.
Third, before you try to log into the hub, make sure you go to your preferences and start hashing at least 1gig of music files. This is the process of choosing and generating your file list and can take some time if you have a very large list. If you try to log in before 1gig is hashed, you'll get auto-kicked.
Fourth, get started in Passive mode before you get fancy and possibly frustrated with Active mode.
The hub is private but not exclusive...it's great to have more users.