The plugin generates a thumbnail from the first image uploaded to a post.
Upload "post_thumb" to the "/wp-content/plugins/" directory
Activate the plugin through the "Plugins" menu in WordPress
Place "<?php post_thumb(); ?>" inside the wp-loop of your template, where ever you want the thumbnail to appear.
A nice way to use this plugin is to link the images to the post by wrapping the plugin template tag into the post URL:
<a href="<?php the_permalink(); ?>" rel="bookmark" title="<?php the_title(); ?>"><?php post_thumb(); ?></a>