on windows (XP, vista, 7...) http://fr.wikipedia.org/wiki/Windows-1252", if your file name contains accent, it doesn't work basically. So use iconv function to convert from utf-8 to cp1252 as bellow :
<?php
$nomfichierinitial=iconv("UTF-8", "CP1252", "C:\\wamp\\www\\tést.txt");
$nomfichierfinal="C:\\wamp\\www\\test.txt";
rename($nomfichierinitial, $nomfichierfinal);
?>