Editing categorie to show thumbnails

Hi,

I installed WordPress and the morning after theme and am now exploring it to see if it will work with my site. I am planning
to move to wordpress, using it as a cms with (a tweaked) tma as theme.

It’s a website with partypictures, one of the categories is named Photo’s. I want that categorie
to show a set of thumbnails. I have allready edited the archive page (archive.php) to display
thumbs instead of the complete posts. The thumbs are now being stacked on top of each other.

The question is:
How do i get the thumbnails to appear 3 in a row, then another 3 and so on.
In total there should be (for example) 12 thumbs in 4 rows each with 3 thumbs a row.

I have enclosed screenshots to help explain what i mean. The code below (of archive.php) results in the first image shown below.
Please let me know if you need more information in order to help me/point me in the right direction.

My archive so far:
https://img247.imageshack.us/img247/441/archiveoz2.jpg

An example of what i am trying to accomplish:
https://img247.imageshack.us/img247/6392/archiveexampleep9.jpg

I am also adding my archive.php:

<?php get_header(); ?>        

        <div id="topbanner_arch" class="column span-14">   <!-- start top banner -->
            <div class="pagetitle">
                // Foto archief
            </div>
        </div>   <!-- end top banner -->

        <div id="arch_content" class="column span-14">   <!-- start home_content -->

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

        	<div class="column span-3 first">

        		<?php if (is_category()) { ?>

            	<h2 class="archive_name"><?php echo single_cat_title(); ?></h2>        

            	<div class="archive_meta">

            		<!--<div class="archive_feed">
            			<?php $cat_obj = $wp_query->get_queried_object(); $cat_id = $cat_obj->cat_ID; echo '<a href="'; get_category_rss_link(true, $cat, ''); echo '">RSS feed for this section</a>'; ?>
       		  </div>

            		<?php $cat_count = $cat_obj->category_count; ?>
            		<div class="archive_number">
            			This category contains <?php echo $cat_count . ($cat_count==1?" post":" posts") ?>
            		</div> -->           

       	  </div>

				<?php } elseif (is_tag()) { ?>

            	<h2 class="archive_name"><?php single_tag_title(); ?></h2>        

            	<div class="archive_meta">

            		<div class="archive_number">
            			This tag is associated with <?php $tag = get_tags(); if ($tag) { $tag = $tag[0]; echo $tag->count; } ?> posts
            		</div>           		

            	</div>

				<?php } elseif (is_day()) { ?>
				<h2 class="archive_name">Archive for <?php the_time('F jS, Y'); ?></h2>

				<?php } elseif (is_month()) { ?>
				<h2 class="archive_name">Archive for <?php the_time('F, Y'); ?></h2>

				<?php } elseif (is_year()) { ?>
				<h2 class="archive_name">Archive for <?php the_time('Y'); ?></h2>

				<?php } ?>

</div>

            <div class="column span-8">
              <?php while (have_posts()) : the_post(); ?>
              <div class="archive_post_block">
<div class="archive_post_meta">
            		<h4 class="archive_title" id="post-<?php the_ID(); ?>"><a>" rel="bookmark" title="Permanent Link to <?php the_title(); ?>"><?php the_title(); ?></a></h4><?php the_time('F j, Y'); ?></div>

   <div class="thumb_archives"><a>" title="<? the_title(); ?>"><img src="<? echo get_post_meta($post->ID, 'thumb_archives', true) ?>" /></a></div>

       		  </div>

            	<?php endwhile; ?>

				<div class="navigation">
					<?php next_posts_link('? Previous') ?> — <?php previous_posts_link('Next ?') ?>

				</div>

				<?php else : ?>

					Lost? Go back to the <a>/">home page</a>.

				<?php endif; ?>

</div>

            <?php get_sidebar(); ?>

        </div>   <!-- start home_content -->

<?php get_footer(); ?>

Thank you in advance for your time and efforts.
Regards,

Tek