how to use wp_query

Hi,

I’ve been using a script to query child pages for my portfolio, I’ve been reading a bit and I think I’ve been using something complex while it can be done easier.

This is the code I’ve been using:

<?php $this_page_id=$wp_query->post->ID; ?>
			<?php query_posts(array('showposts' => 12, 'orderby' => 'menu_order', 'order' => 'ASC', 'post_parent' => '9', 'post_type' => 'page')); while (have_posts()) { the_post(); ?>
                <?php if ( get_post_meta($post->ID, "post-img", true) ) { ?>
                <?php } else { ?>
			<!-- DIV's, headers and paragraphs go here -->
                <?php } ?>
			<?php } ?>

Now i’ve been testing this one below and it seems to work just fine:

<?php query_posts(array('showposts' => 20, 'orderby' => 'menu_order', 'order' => 'ASC', 'post_parent' => 9, 'post_type' => 'page')); while (have_posts()) { the_post(); ?>
    <!-- DIV's, headers and paragraphs go here -->
<?php } ?>

To be honest I’ve been using the first one since I got into WordPress and wasn’t sure what it did exactly, so if anyone can tell me the difference between the two, and if it’s safe to use the 2nd one.

Thanks!
Mathieu