admin of the site has access to every corner of the site.
access to all the pms, mails sent/received, everything..
privacy is out of question.
you don't really need to be registered with the discussion board, if they've lifted off the restriction where anonymous user can post, they can see all the details of IP.
I don't know what ISP you are with, mine is COMCAST and they literally are eavesdropping on me.
So, we don't really have any privacy on current internet :D 

I'm technically sound and have background in penetration on remote systems. I was elusive and I've learned many things while I was evading bans on irc chats and forums. That really made some of those MOD really mad and I remember finally making me mod in their irc.

All I can suggest for you now is that you can rely on distributed ip sharing services like TOR. It will hide your true IP logs but it's not foolproof but will give hardtime for whoever is trying to investigate. They need next level of access to investigate. But the layer pretty much covers up your identity online.