<?
session_unset();
session_destroy();
session_start();
session_register(uniqid(rand()));
if ($error)
{ //$ucolor="red"; $upasswd="red";
echo "<center>";
echo "<font race=\"verdana\" size=\"5\" color=\"red\"><b>{ Access Denied }</b><br></center><P>";
}
else if ($error=="logout")
{
echo "<center>";
echo "<font race=\"verdana\" size=\"5\" color=\"red\"><b>{ Log in }</b><br></center><P>";
}
.
.
.
.
?>

(it is simple for now)
<?
session_start();
  if($Submit)
  {if(($ausername=="eric")&&($apasswd=="dfeef"))
    {$logged_user = $ausername;
      session_register("logged_user");
      header("Location: list.php");
      exit;
    }
    else if(($ausername=="admin")&&($apasswd=="pooolk"))
    {
      $logged_user = $user_name;
      session_register("logged_user");
      header("Location: adminpanel.php");
      exit;
    }
  else
   {header("Location: index.php?error=$logid&user=$ausername");
    exit;
   }
}
?> 

<?
  unset($logged_user);
  session_start();
  session_register($logged_user);
  if(!isset($logged_user))
  { $err=1;
    header("Location:index.php?error=$err");
    exit();
  }
....
.
?>

<?
session_start();
session_unset();
session_destroy();
if (session_destroy())
{$err="logout";
header("Location:index.php?error=$err");
exit();}
?>