Since iWeb content stays in its own folder, you can create another folder and do the one-click installs for the calendar and bulletin board. Your domain directory will look like:
/home/USER/domain.com/all your iWeb files go right here (not a folder)
Then create Hyperlinks in iWeb to point to http://yourdomain.com/calendar (and phpbb)
To protect the site, see this Wiki entry:
If you password protect /home/USER/domain.com, then all directories under it will fall under the same protection.