Short:
In a class "if ($this->arr[$keyname] != 0);" will allways be false.

Long:
<?
class Auth {
  var $AuthTblCols = array('login'      => 'login',
                           'passwd'     => 'passwd',
                           'access_lvl' => 0,
                           'last_login' => 0);

//.... snip ....
   function ColOK($colname, $str) {
    print_r("<pre>ColOK:");  var_dump($this->AuthTblCols[$colname]);print_r("</pre>"); 
/* returns string 'access_lvl' (see under) */
      if (!empty($this->AuthTblCols[$colname]) &&

          !($this->AuthTblCols[$colname] == 0)
/* The Line above will allways evaluate false!!?!
at first I had:
$this->AuthTblCols[$colname] != 0
But it also evaluates false.*/
      ) {
print_r("HERE");
         return (empty($str)?true:$str);
      }
      return false;
   }
    function somefunc() {
// a func inside the class will call ColOK()
      if (!$str = $this->ColOK('access_lvl', 
                               "somestring I want returned")) echo "Not ok";
//.... snip ....
}

$auth = new Auth();
$auth->AuthTblCols = array('login'      => 'login',
                           'passwd'     => 'passwd',
                           'access_lvl' => 'access_lvl',
                           'last_login' => 'last_login');
if (!$auth->A_func_that_will_run_somefunc()) {
  echo "Invalid login/password";
  exit;
}
?>