<?php 
  $handle=opendir('.'); 
  while ($file = readdir($handle)) { 
     if ($file != "." && $file != "..") { 
          echo "$file\n"; 
      } 
  }
 closedir($handle); 
?>

This script the same one from php manual.
in php 4.0 It's was ok.
but in php 4.0.1, sometimes show following messages.

1 is not a valid Directory resource in /home/silver/public_html/readdir.php3 on line 5