Highlighting menu

I am trying to build a menu which highlights the menu when you are viewing the page, I search the internet and tried numerous tutorials but have not been able to get anything to work.
Here the page:

<http://www.fireseedproductions.co.uk/office/description

Here the menu code I am using.

<div class="pagemenu">
<ul>
<?php if($post->post_parent) $children = wp_list_pages("sort_column=menu_order&title_li=&child_of=0".$post->post_parent."&echo=1");
else	$children = wp_list_pages("sort_column=menu_order&title_li=&child_of=0".$post ->ID."&echo=2");
if ($children) { ?>
<li><?php echo $children; ?></ul></li>
<?php } ?></ul>					</div>			<div>
<h2><a href="<?php the_permalink(); ?>" title="<?php the_title(); ?>">

Any help would be appreciated.