I would like to set up a strictly private forum, available only to pre-approved members of an organization. Is there a way to remove and disable the links for Register, Search, Statistics, and Manual, so that anyone who is not a member of the group cannot register or see user profiles? I would also like to put a message on the index page informing anyone who happens to land there that it is a private forum, but I am not sure which file(s) to edit to accomplish this. Thanks.

Configuration file setup_options.php has settings that allow the whole forum being password protected from outside world. It can be achieved by placing inside setup_options.php these two:

$protectWholeForum = 1;
$protectWholeForumPwd = 'passwordgoeshere';

If you inform your forum's users that password, they can open the forum.

Login form is inside templates folder and is named protect_forums.html, which can of course also include other information, like a message that says this forum is for pre-approved members etc.

That wasn't really what I had in mind, because the users will need two passwords, one for the forum, and a separate one for their individual accounts. I don't want to be kept busy emailing the password out to people who lose it. :-) At least it works until I can hopefully figure out a better solution. Thanks.

I figured this out by copying and pasting from a couple of posts on this forum.
In case anyone else wants to do something similar, I put the following lines into my bb_plugins.php file:

-----------------------------------------------------

if(($user_id==0) and ($action=='register' or $action=='registernew')){
$enableNewRegistrations=FALSE;
echo load_header();
echo ParseTpl(makeUp('guest_denied'));
$endtime=get_microtime();
$totaltime=sprintf ("%01.3f", ($endtime-$starttime));
if(isset($includeFooter) and $includeFooter!='') include($includeFooter); else echo ParseTpl(makeUp('main_footer'));
exit;
}

if($user_id==0 and $action=='search'){
echo load_header();
echo ParseTpl(makeUp('guest_denied'));
$endtime=get_microtime();
$totaltime=sprintf ("%01.3f", ($endtime-$starttime));
if(isset($includeFooter) and $includeFooter!='') include($includeFooter); else echo ParseTpl(makeUp('main_footer'));
exit;
}

if($user_id==0 and $action=='stats'){
echo load_header();
echo ParseTpl(makeUp('guest_denied'));
$endtime=get_microtime();
$totaltime=sprintf ("%01.3f", ($endtime-$starttime));
if(isset($includeFooter) and $includeFooter!='') include($includeFooter); else echo ParseTpl(makeUp('main_footer'));
exit;
}

if($user_id==0 and $action=='manual'){
echo load_header();
echo ParseTpl(makeUp('guest_denied'));
$endtime=get_microtime();
$totaltime=sprintf ("%01.3f", ($endtime-$starttime));
if(isset($includeFooter) and $includeFooter!='') include($includeFooter); else echo ParseTpl(makeUp('main_footer'));
exit;
}

-----------------------------------------------------

Then I made a page called guest_denied.html with a message saying that it was a private forum, and saved it in my templates directory. Now an unregistered user will still see the menu links, but will only get the error message when they click on one.

You can compress this into much smaller code:

Also, remove all the proper {$l_menu[...]} elements from templates/main_header.html i.e.

$l_menu[1] for 'Search'
$l_menu[2] for 'Register'
$l_menu[3] for 'Stats'
$l_menu[4] for 'Manual'

Looks like a valid approach, specially if it works for you that way.
Good luck!

Thanks. I will try your version. I thought there must be a better, shorter way, but since I don't know too much about php and it worked as is, I didn't want to risk breaking something with a typo. I will keep the menu elements though, because I do want them to be available to anyone who is registered and logged in, with the possible exception of "Register", since they are already registered.

For disabling Registration option, you did it right before - but must apply it in setup_options.php for all users, not just guests.

I.e. just set

in setup_options.php.