This works. I have the timeout settings on 500 seconds in the vbulletin board, so the working skript looks now like that: (remember the right path to the admin/config file!)
Code:
<?
require("admin/config.php");
$db=mysql_connect($servername,$dbusername,$dbpassword);
mysql_select_db($dbname);
$datecut = time()-500;
$loggedins=mysql_query("SELECT COUNT(userid) AS users FROM session WHERE lastactivity>$datecut AND userid>0",$db) or die ("oops");
while($loggedin = mysql_fetch_array($loggedins))
$membersonline=number_format($loggedin[users]);
$guestsloggedins=mysql_query("SELECT COUNT(userid) AS users FROM session WHERE lastactivity>$datecut AND userid=0",$db) or die ("oops");
while($guestsloggedin = mysql_fetch_array($guestsloggedins))
$guestsonline=number_format($guestsloggedin[users]);
$users=mysql_query("SELECT COUNT(userid) AS registeredusers FROM user",$db) or die ("double oops");
while($user = mysql_fetch_array($users))
$totalusers=number_format($user[registeredusers]);
echo "<font face=arial size=2>
We have a total of $totalusers registered users. There are currently $membersonline members and $guestsonline guests online.</font>
";
?>