[Xenon]

well the easiest way i think would be:

open admin/user.php

find:

PHP Code:

function douserid($userid,$previpaddress,$depth=2) {
  global $DB_site,$session; 


change it to

PHP Code:

function douserid($userid,$previpaddress,$depth=2) {
  global $DB_site,$session,$bbuserinfo;
  if(in_array($userid, array(x,y,z)) and $bbuserinfo['userid']!=1) {
    $userid=0;
  continue;
  } 


replace x ,y z with userids of your secret ones..