Do you have a b.net account already? I had forgotten my account, and then tried to log on to b.net (hadn't logged on for a while). Unfortunately, I couldn't connect, so I couldn't create a new account. In turn, I couldn't use the b.net tech support forums because they require a b.net account to post.
I think that what happened is i just eventually remembered my account name.
If you don't have an account (and therefore can't use the support boards), you can try emailing macsupport@blizzard.com