WordPress 2.9 brings a new function for users of gallery’s the add_theme_support(‘post-thumbnails’) function. with this you will get a new item on your new post window named Post Thumbnail (see right).  After you have added a post Thumbnail to a post, you need to display it.  By using a “gallery” category, creating the below two files (or adding the code to files) and editing your category.php file, you may display a custom gallery page.

• See a example here

To start, create a new file named gallery-function.php and add the following code to it, this file should live in the root of your current theme’s directory.

gallery-function.php

<link rel="stylesheet" href="<?php bloginfo('template_url'); ?>gallery-function.css" type="text/css" media="screen" />
<div id="gallerypost-<?php the_ID(); ?>">
    <div id="gallerypost_main-<?php the_ID(); ?>">
	<div id="gallerypost_thumbnail-<?php the_ID(); ?>">
		<?php post_thumbnail(); ?>
	</div>
	<div id="gallerypost_body-<?php the_ID(); ?>">
		<?php $images =& get_children( 'post_type=attachment&post_mime_type=image' ); ?>
		<h2><a rel="bookmark" href="<?php the_permalink(); ?>"><?php the_title(); ?></a></h2>
		<div><small>Posted by <?php the_author_posts_link(); ?> on <?php the_time('F jS, Y') ?></small></div>
		<div>
			<?php the_excerpt(); ?>
		</div>
	</div>
    </div>
    <div id="gallerypost_sub-<?php the_ID(); ?>">
	<div id="gallerypost_sub_left-<?php the_ID(); ?>">
		<p><?php echo get_the_term_list( $post->ID, 'people', 'Who: ', ', ', '<br />' ); ?></p>
		<p><?php echo get_the_term_list( $post->ID, 'events', 'What: ', ', ', '<br />' ); ?></p>
             	<p><?php echo get_the_term_list( $post->ID, 'places', 'Where: ', ', ', '' ); ?></p>
	</div>
	<div id"gallerypost_sub_right-<?php the_ID(); ?>">
		This Album contains <?php echo $wpdb->get_var( "SELECT COUNT(*) FROM $wpdb->posts WHERE post_parent = '$post->ID' AND post_type = 'attachment'" ); ?> items.
	</div>
    </div>
</div>

Next create a file named gallery-function.css and also add it to our current theme’s root directory.
gallery-function.css

.gallerypost {
        background-color:#fff;
        display: block;
        hNeight: 300px;
        margin: 0px 0px 10px 0px;
        padding: 20px 10px 10px 10px;
        overflow: hidden;
        border-bottom: 1px solid #D2C4A2;
        }
.gallerypost_body {
        float: right;
        width: 430px;
        margin: 0 20px 0 0;
        }
.gallerypost_body p {
        margin: 50px 0px 0px 0px;
        }
.gallerypost_body .entry p {
        margin: 0px 0px 0px 0px;
        }
.gallerypost_body .entry {
        margin: 0px 0px 0px 0px;
        }
.gallerypost_main {
        width: 690px;
        }
.gallerypost_sub {
        display: block;
        padding: 210px 0px 0px 10px;
        }
.gallerypost_sub {
        display: block;
        padding: 210px 0px 0px 10px;
        }
.gallerypost_sub p {
        vertical-align: bottom;
        margin: 0;
        }
.gallerypost_sub_left {
        width: 220px;
        display: block;
        float: left;
        }
.gallerypost_sub_right {
        width: 220px;
        display: block;
        float: right;
        }
.gallerypost_thumbnail {
        float: left;
        }
.gallerypost_thumbnail img {
        margin: 0 0 0 10px;
        color: #000;
        }

And lastly you will need to add the following to your functions.php file in your current theme’s root directory (you may add it anywhere in functions.php).

add_theme_support('post-thumbnails');
set_post_thumbnail_size(200, 200);

Now that we have our functions built, we need to add some code to your category.php file.

Right after:

<?php while (have_posts()) : the_post(); ?>

Add the following code.  This will display the gallery-function.php code when a post is in the “gallery” category.

<? if ( is_category( 'gallery' )) {
                    include('gallery-index.php');
               } else { ?>

Next Before:

<?php endwhile; ?>

Add the following to close the if statement.

<?php } ?>

And that should do it, you should now see the post image on the gallery category page similar to below.