I had some problems with the params "frozen_nick", although I write it to "true" it was still possible to modify the nick name. So I hadded this script on chat.html.tpl.php file :
replace line n°16
<input id="<?php echo $prefix; ?>handle" type="button" title="<?php echo _pfc("Enter your nickname here"); ?>" value="<?php echo $u->nick; ?>" onclick="pfc.askNick('');" />
by
<?php if (!$c->frozen_nick) { ?>
<input id="<?php echo $prefix; ?>handle" type="button" title="<?php echo _pfc("Enter your nickname here"); ?>" value="<?php echo $u->nick; ?>" onclick="pfc.askNick('');" />
<?php } else { ?>
<input id="<?php echo $prefix; ?>handle" type="button" title="<?php echo $u->nick; ?>" value="<?php echo $u->nick; ?>" />
<?php } ?>