Basic PHP script/syntax help in modifying sidebar

My objective is ultimately this:
If this is a page then show sub-nav, if not show the normal widgets.

Here’s my script so far, I realise I need to add an else in there somewhere but my attempts have failed probably due to my lack of coding experience:

<?php
    // This creates a sub navigation containing the child pages.
    if ( is_page() ) { ?>

<?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 class="childnav">
<h2>
<?php
$parent_title = get_the_title($post->post_parent);
echo $parent_title;
?>
</h2>

<ul>
<?php echo $children; ?>
</ul>
</div>

<?php } } ?>
/*an else needs to replace the line above but doing so breaks the code*/
<ul>

<?php
	/* When we call the dynamic_sidebar() function, it'll spit out
	 * the widgets for that widget area. If it instead returns false,
	 * then the sidebar simply doesn't exist, so we'll hard-code in
	 * some default sidebar stuff just in case.
	 */
	if ( ! dynamic_sidebar( 'primary-widget-area' ) ) : ?>

			<li>
				<?php get_search_form(); ?>
			</li>

			<li>
				<h3><?php _e( 'Archives', 'twentyten' ); ?></h3>
				<ul>
					<?php wp_get_archives( 'type=monthly' ); ?>
				</ul>
			</li>

			<li>
				<h3><?php _e( 'Meta', 'twentyten' ); ?></h3>
				<ul>
					<?php wp_register(); ?>
					<li><?php wp_loginout(); ?></li>
					<?php wp_meta(); ?>
				</ul>
			</li>

		<?php endif; // end primary widget area ?>
			</ul>