mlnosp

Thank you MadsK for the great idea of using post_parent. Thank to you I could solve my problem like this without requiring any extra template pages:

if( $post->post_parent )
		$page_id = $post->post_parent;
	else
		$page_id = $post->ID;
	wp_list_pages("child_of=$page_id&title_li=");

Wow cool thing, this is exactly what I am looking for, thank you very much!