paradigmshiftkey

Nevermind. I got it to work with a slight alternation:

<?php $posts = query_posts( $query_string . '&meta_key=date_start&orderby=meta_value_num&order=desc' ); ?>

Above this in my category-calendar.php page, duped from archive.php:

<?php if ( have_posts() ) : ?>

			<?php rewind_posts(); ?>

			<div class="posts" id="posts">

				<?php while ( have_posts() ) : the_post(); ?>

					<?php get_template_part( 'content', get_post_format() ); ?>

				<?php endwhile; ?>