Well for whatever pages you wish to be members only, enclose the code in this format:
PHP:
if($isloggedin == "yes"){
// Code for members
}
else{
$article_title = $accden;
$article_content = $reqlogin;
}
Otherwise, you will have to remove the if-condition ($isloggedin = "yes") so that guests can view the page. One good example is levelup.php, which does not have restriction for members. Just go to whatever php files/pages you want your guests to view, remove the if/else statement to check user login. This may take a while though, considering the script disallows guests to view most content.
This I am not quite sure, you have to give a try and see if this happens. The script was designed to block guests from viewing pages, not certain what occurs if you remove the restriction.