Need to stop posts nesting on category page

Hi There!

I have created a category template page with the aim of displaying only posts belonging to the newsletters category.

I am using the basic WordPress loop, but the posts are displayed in a nested manner i.e. each newer post appears above and to the left of the previous one like this:

Post 1 ———————————–
———-Post 2 —————————-
—————–Post 3 ———————-

I am using the following code

<br />
<?php get_header(); ?><br />
<div id="content" ><br />
	<div id="main"><br />
		<h1>Newsletters</h1><br />
		<?php if ( have_posts() ) : while ( have_posts() ) : the_post(); ?><br />
			<h3><?php the_title(); ?></h3><br />
			<h4>Posted on <?php the_time('F jS, Y') ?></h4><br />
			<p><?php the_content(__('(more...)')); ?></p><br />
		<?php endwhile; else: ?><br />
			<p><?php _e('Sorry, no posts matched your criteria.'); ?></p><br />
		<?php endif; ?><br />
	</div><br />
<?php get_sidebar(); ?><br />
</div><br />
<?php get_footer(); ?><br />

I am sure it’s something very obvious to you out there, but please help!