Lockdown BP installation?


Hey Guys, how can I lockdown the entire buddypress installation, but let users to register?

I mean, I´d like when someone tries to access the bp site the wordpress login page appears with the registration link below it, if I´m not a user yet, I can register...

Another thing, I really would like to let just some e-mail domains to register, is there a way to do that?

Thanks guys!