How to display child-pages only in the sidebar?

Hi @ll,

It’s my first attempt to use WP, thanks in advance for your patience..
My challenge is ‘hiding child-pages from the main-navi and displaying their links in the sidebar’.

theme: StudioPress 1.2 (for the nice main-nav)
I tried several plugins but some won’t work or just hide the child-pages in the sidebar – the opposite effect I am looking for.
plugins:
page-link-manager (no effect)
pagemash (update timeout, -“-)
exclude-pages (sidebar only)
flexi-pages ( -“- )
CSS:
.page-item-23 {display: none;} (sidebar only)

I read about
<?php wp_list_pages('exclude=23' ); ?>
but either I put it wrong or it doesn’t match with the theme…

the nav part of header.php:

<div id="nav">
<?php function get_the_pa_ges() {
  global $wpdb;
  if ( ! $these_pages = wp_cache_get('these_pages', 'pages') ) {
     $these_pages = $wpdb->get_results('select ID, post_title from '. $wpdb->posts .' where post_status = "publish" and post_type = "page" order by ID');
   }
  return $these_pages;
 }

 function list_all_pages(){

$all_pages = get_the_pa_ges ();
foreach ($all_pages as $thats_all){
$the_page_id = $thats_all->ID;

if (is_page($the_page_id)) {
  $addclass = ' class="current_page"';
  } else {
  $addclass = '';
  }
$output .= '<li' . $addclass . '><a href="'.get_permalink($thats_all->ID).'" title="'.$thats_all->post_title.'"><span>'.$thats_all->post_title.'</span></a></li>';
}

return $output;
 }
?>
<ul>

<?php
if (is_home()) {
  $addclass = ' class="current_page"';
  } else {
  $addclass = '';
  }
echo "<li" . $addclass . "><a href='" . get_option('home') . "' title='Home'><span>Home</span></a></li>";
echo list_all_pages();?>
</ul>
<div class="cleared"></div>
</div> <!-- Closes Nav -->

Any hints? Thx! ??