There is no passworded forums in 7.0 like there was in UBB.C (however it was a great feature and I for one quite loved it).
Viewing the board in general with a password, I don't think I've ever seen in the first place; you could try just assigning a password to the directory your forum is installed in through apache (see the apache documentation for htpasswd), it'd pop up a password box for a user to input a username and password in order to access your threads install... although i think the registration queue and no guest viewing of forums in 7 would be a better way of going about this.
