Copy loop.php and call the new copy loop-category.php
. Edit this new file and replace:
<?php if ( post_password_required() ) : ?>
<?php the_content(); ?>
<?php else : ?>
<div class="gallery-thumb">
<?php
$images = get_children( array( 'post_parent' => $post->ID, 'post_type' => 'attachment', 'post_mime_type' => 'image', 'orderby' => 'menu_order', 'order' => 'ASC', 'numberposts' => 999 ) );
$total_images = count( $images );
$image = array_shift( $images );
$image_img_tag = wp_get_attachment_image( $image->ID, 'thumbnail' );
?>
<a class="size-thumbnail" href="<?php the_permalink(); ?>"><?php echo $image_img_tag; ?></a>
</div><!-- .gallery-thumb -->
<p><em><?php printf( __( 'This gallery contains <a %1$s>%2$s photos</a>.', 'twentyten' ),
'href="' . get_permalink() . '" title="' . sprintf( esc_attr__( 'Permalink to %s', 'twentyten' ), the_title_attribute( 'echo=0' ) ) . '" rel="bookmark"',
$total_images
); ?></em></p>
<?php the_excerpt(); ?>
<?php endif; ?>
with <?php the_content(); ?>
.