The following code, when pasted into the template sidebar, works perfectly, but doesn't work when using this plugin.
<?php
//show parent page
$parent_title = get_the_title($post->post_parent);?>
<a href="<?php echo get_permalink($post->post_parent) ?>" class="parent"><?php echo $parent_title;?></a>
<?php
//show child pages
if($post->post_parent)
$children = wp_list_pages("title_li=&child_of=".$post->post_parent."&echo=0");
else
$children = wp_list_pages("title_li=&child_of=".$post->ID."&echo=0");
if ($children) { ?>
<ul id="subnav">
<?php echo $children; ?>
</ul>
<br clear="all" />
<?php } ?>