Easy way to lock down forum!

Any ideas on the easy way to lock down a whole forum...

Basically I have an archive that is using punbb. But I dont want to go through and change each forum to read only. Any easy way to make it open but no posting or logging in.

Thanks in advance.

EDIT:
Fixed! or Sorted!
I just changed login.php so only old admins can log in.

if ($group_id <> 1)
{
    header('Location: index.php');
    exit;
}

Guest posting is closed on all forums so all good.