custom tag get_post_meta(),how to retrieve several posts at a time

Hello,
I am trying to customize a plugin,where custom tag “get_post_meta()” is used.
The code is as follows:
<?php query_posts(‘showposts=5’); ?>
<?php if (have_posts()) : while (have_posts()) : the_post(); ?>
<h2>” title=”<?php the_title(); ?>”>
<?php the_title(); ?></h2>
<?php the_excerpt(); ?>
<?php $gallery = get_post_meta($post->ID, ‘Thumbnail’, $single = true); ?>
<img src=”<?php echo $gallery; ?>”>`

I tried with making the parameter false and to retrieve array values:
and echo them.But its not happening.can any one suggest me to have several posts at a time?
Thanks