wp_list_pages sub sub-pages

I’ve got a problem with listning the parent and its sub-pages when on a sub-sub-page.

My current code is this:

<?php
			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) { ?>
			<div id="subnav">
				<div class="subtop"></div>
					<div class="subcontent">
						<ul>
						<?php echo $children; ?>
						</ul>
					</div>
				<div class="subbottom"></div>
			</div>
			<?php } ?>

What i want to do is have the menu show the same all the time even when on a SUB-SUB-page. Now it’s just the same when on the top-parent and when on a child. Not when on a child of a child …

How can i modify that code the display the parent and its childs even when on a child of a child?

Please help. ??

Regards,
Tommie Hansen