If you are getting permission error while installing CiviCRM on xampp then, its is default CiviCRM user permission error,

Just comment the following code in "sites/all/modules/civicrm/install/index.php" See Below:

Find below code on index.php usually at line no 268, comment the whole If condition :

/* if ((!function_exists('user_access')) || (!user_access('administer site configuration'))) {
    $errorTitle = ts("You don't have permission to access this page");
    $errorMsg = ts("The installer can only be run by a user with the permission to administer site configuration.");
    errorDisplayPage($errorTitle, $errorMsg);
    exit();
  } */

Now relaod the page : sites/all/modules/civicrm/install/index.php .