[MeTaL_oRgY]

well, I don't know if it'll be of much help.. but try what I do:

First of all, install the comment script you like the most, it doesn't matter which one you choose.

After you've got it up and running, you'll have to set permissions to the key file.. the key file is the one that'll allow people to post a comment. It can be either the html (or php) that you call to print the comment form on your page or the php file that processes the information entered at the form. This depends on the script you're using (which I recommend that it DO NOT require registration, since you'll need to hack it a little more...).

Now that you have located the file, you'll now need to include the global file to that page.

<?php  include ('../foro/global.php'); ?>

add this at the very top of the page. Now comes the tricky part. Add this code below the include command:

//change xx with the Guest Group ID.
if($bbuserinfo['usergroupid']==xx){
echo "Please log-in or register!";
} else {
//the rest of the code goes here

and don't forget to close the script adding one last } to the end of your page.. so the final php would look like this:

<?php  include ('../foro/global.php');
//change xx with the Guest Group ID.
if($bbuserinfo['usergroupid']==xx){
echo "Please log-in or register!";
} else {
//the rest of the code goes here
//code
//code
//code
//lol
}
?>

YOu'll hve to experiment with it a bit.. but it works fine for me ...

NOTE Remember that if you have HTML between the

} else {

and the final }, you'll have to add backslash (\) befor every quote (") you have .

EDIT
Damn. I forgot one thing... before including global.php you must modify it a bit... every url the file has is like this:

admin/functions.php

You must change it so it looks like this:

/home/user/public_html/forum/admin/functions.php

there aren't much of this.. so it's not such a big deal :P