This code into the comment.tpl.php make a link to the parent comment:

<?php if ($comment->pid): 
$parent_comment = db_result(db_query('SELECT subject FROM {comments} WHERE cid = %d AND status = %d', $comment->pid, COMMENT_PUBLISHED));
print  '<a href="' . $node_url . '#comment-' . $comment->pid.'" title="' . $parent_comment .'" >' . t('Pre') . '</a>';
endif; ?>