Corrigiendo....
Donde debe quedar es en index.template.php
Si deseas que esté al lado de los botones "powered by php, powered by mysql", debes modificar esta parte:
<table cellspacing="0" cellpadding="3" border="0" align="center" width="90%" class="tborder">
<tr style="background-color: #ffffff;">
<td width="28%" valign="middle" align="right">
<a href="http://www.mysql.com/"><img src="', $settings['images_url'], '/mysql.gif" alt="', $txt['powered_by_mysql'], '" width="88" height="31" border="0" /></a>
<a href="http://www.php.net/"><img src="', $settings['images_url'], '/php.gif" alt="', $txt['powered_by_php'], '" width="88" height="31" border="0" /></a>
</td>
<td width="44%" valign="middle" align="center">
', theme_copyright(), '
</td>
<td width="28%" valign="middle" align="left">
<a href="http://validator.w3.org/check/referer"><img src="', $settings['images_url'], '/valid-xhtml10.gif" alt="', $txt['valid_xhtml'], '" width="88" height="31" border="0" /></a>
<a href="http://jigsaw.w3.org/css-validator/check/referer"><img src="', $settings['images_url'], '/valid-css.gif" alt="', $txt['valid_css'], '" width="88" height="31" border="0" /></a>
</td>
</tr>
</table>';