<?php
if(is_category()){ ?>
<div id="left-column">
<?php if (have_posts()) : while(have_posts()) : $i++; if(($i % 2) == 0) : $wp_query->next_post(); else : the_post(); ?>
<div id="post-<?php the_ID(); ?>" <?php post_class(); ?>>
			<h2 class="entry-title"><a href="<?php the_permalink(); ?>" title="<?php printf( esc_attr__( 'Permalink to %s', 'premiumqualitythemes' ), the_title_attribute( 'echo=0' ) ); ?>" rel="bookmark"><?php the_title(); ?></a></h2>
<div class="entry-content">
				<div style="float: left; margin-right: 5px;">
				<?php the_post_thumbnail( array(150,150) ); ?>
            	</div>
				<?php the_content(); ?>
</div></div>
<?php endif; endwhile; else: ?>
<div>Alternate content</div>
<?php endif; ?>
</div>

<?php $i = 0; rewind_posts(); ?>
<div id="right-column">
<?php if (have_posts()) : while(have_posts()) : $i++; if(($i % 2) !== 0) : $wp_query->next_post(); else : the_post(); ?>

<div id="post-<?php the_ID(); ?>" <?php post_class(); ?>>
			<h2 class="entry-title"><a href="<?php the_permalink(); ?>" title="<?php printf( esc_attr__( 'Permalink to %s', 'premiumqualitythemes' ), the_title_attribute( 'echo=0' ) ); ?>" rel="bookmark"><?php the_title(); ?></a></h2>
<div class="entry-content">
				<div style="float: left; margin-right: 5px;">
				<?php the_post_thumbnail( array(150,150) ); ?>
            	</div>
				<?php the_content(); ?>
</div></div>

<?php endif; endwhile; else: ?>
<div>Alternate content</div>
<?php endif; } ?>
</div>