misterfade, if you know how to connect to your MySql database this query gets the registered number of users on your site:
PHP Code:
$result = mysql_query("SELECT * FROM user");
if(!($result)) {
print "Useronline Select Error > ";
}
$totalusers = mysql_num_rows($result);
echo "<p class=\"feed\"><b>Total members:</b> $totalusers<br />";
Very basic, seen in action
here.