Issues displaying post images with custom fields

I’ve designed a blog index page that will display the five latest posts. Each post will include an image, post title, date/comments and an excerpt. So far, I have the following code, along with a custom field in each post with name=thumbnail and value= image path. The images displayed won’t appear in the posts, so they can be stand alone images that only appear on the blog index page.

<div class="post_wrap">
			<h2 class="heading">Recent Posts</h2>

            	<div style="border-bottom:1px dotted #C0C0C0; margin-bottom:10px; margin-left:14px; margin-right:14px; padding:0px
                0px 10px 0px; clear:both;"></div>

            <div class="post_img">
				<?php $recent = new WP_Query("cat=6&showposts=1"); while($recent->have_posts()) : $recent->the_post();?>
				<?php if( get_post_meta($post->ID, "Thumbnail", true) ): ?>
				    <img style="float:left;margin:0px 5px 0px 0px;" src="<?php echo get_post_meta($post->ID, "Thumbnail", true); ?>"
                    alt="alt text" />
				<?php else: ?>
				    <img style="float:left;margin:0px 5px 0px 0px;"  src="<?php bloginfo('template_url'); ?>/images/thumbnail.jpg" alt
                    ="Default Thumbnail" />
				<?php endif; ?>
             </div><!--end post_img-->

             <div class="post_content">
				<b><a href="<?php the_permalink() ?>" rel="bookmark"><?php the_title(); ?></a></b>
                	<div class="stamp"><?php the_time('F jS, Y') ?><!-- by <?php the_author() ?> --> | <?php
					comments_popup_link(
					'No
					Comments »'
					, '1 Comment »', '% Comments »'); ?></div>
				<div class="excerpt"><?php if ($post->post_excerpt != "" ) {the_excerpt();}else {the_content_rss('', FALSE, '', 60);}
				?><a href="<?php the_permalink() ?>" rel="bookmark" title="Permanent Link to <?php
					the_title_attribute(); ?>"> READ MORE</a>
                </div><!--end excerpt-->   

              </div><!--end post_content-->

				<div style="border-bottom:1px dotted #C0C0C0; margin-bottom:10px; margin-left:14px; margin-right:14px; padding:0px
                0px 10px 0px; clear:both;"></div>

				<?php endwhile; ?>

What am I doing wrong?