WordPress/wp-admin/themes.php

<?php
require_once('admin.php');

if ( isset($_GET['action']) ) {
	check_admin_referer('switch-theme_' . $_GET['template']);

	if ('activate' == $_GET['action']) {
		if ( isset($_GET['template']) )
			update_option('template', $_GET['template']);

		if ( isset($_GET['stylesheet']) )
			update_option('stylesheet', $_GET['stylesheet']);

		do_action('switch_theme', get_current_theme());

		wp_redirect('themes.php?activated=true');
		exit;
	}
}

$title = __('Manage Themes');
$parent_file = 'themes.php';
require_once('admin-header.php');
?>

<?php if ( ! validate_current_theme() ) : ?>
<div id="message1" class="updated fade"><p><?php _e('The active theme is broken.  Reverting to the default theme.'); ?></p></div>
<?php elseif ( isset($_GET['activated']) ) : ?>
<div id="message2" class="updated fade"><p><?php printf(__('New theme activated. <a href="%s">View site &raquo;</a>'), get_bloginfo('url') . '/'); ?></p></div>
<?php endif; ?>

<?php
$themes = get_themes();
$ct = current_theme_info();
?>

<div class="wrap">
<h2><?php _e('Current Theme'); ?></h2>
<div id="currenttheme">
<?php if ( $ct->screenshot ) : ?>
<img src="<?php echo get_option('siteurl') . '/' . $ct->stylesheet_dir . '/' . $ct->screenshot; ?>" alt="<?php _e('Current theme preview'); ?>" />
<?php endif; ?>
<h3><?php printf(__('%1$s %2$s by %3$s'), $ct->title, $ct->version, $ct->author) ; ?></h3>
<p><?php echo $ct->description; ?></p>
<?php if ($ct->parent_theme) { ?>
	<p><?php printf(__('The template files are located in <code>%2$s</code>.  The stylesheet files are located in <code>%3$s</code>.  <strong>%4$s</strong> uses templates from <strong>%5$s</strong>.  Changes made to the templates will affect both themes.'), $ct->title, $ct->template_dir, $ct->stylesheet_dir, $ct->title, $ct->parent_theme); ?></p>
<?php } else { ?>
	<p><?php printf(__('All of this theme&#8217;s files are located in <code>%2$s</code>.'), $ct->title, $ct->template_dir, $ct->stylesheet_dir); ?></p>
<?php } ?>
</div>

<h2><?php _e('Available Themes'); ?></h2>
<?php if ( 1 < count($themes) ) { ?>

<?php
$style = '';

$theme_names = array_keys($themes);
natcasesort($theme_names);

foreach ($theme_names as $theme_name) {
	if ( $theme_name == $ct->name )
		continue;
	$template = $themes[$theme_name]['Template'];
	$stylesheet = $themes[$theme_name]['Stylesheet'];
	$title = $themes[$theme_name]['Title'];
	$version = $themes[$theme_name]['Version'];
	$description = $themes[$theme_name]['Description'];
	$author = $themes[$theme_name]['Author'];
	$screenshot = $themes[$theme_name]['Screenshot'];
	$stylesheet_dir = $themes[$theme_name]['Stylesheet Dir'];
	$activate_link = wp_nonce_url("themes.php?action=activate&amp;template=".urlencode($template)."&amp;stylesheet=".urlencode($stylesheet), 'switch-theme_' . $template);
?>
<div class="available-theme">
<h3><a href="<?php echo $activate_link; ?>"><?php echo $title; ?></a></h3>

<a href="<?php echo $activate_link; ?>" class="screenshot">
<?php if ( $screenshot ) : ?>
<img src="<?php echo get_option('siteurl') . '/' . $stylesheet_dir . '/' . $screenshot; ?>" alt="" />
<?php endif; ?>
</a>

<p><?php echo $description; ?></p>
</div>
<?php } // end foreach theme_names ?>

<?php } ?>

<?php
// List broken themes, if any.
$broken_themes = get_broken_themes();
if ( count($broken_themes) ) {
?>

<h2><?php _e('Broken Themes'); ?></h2>
<p><?php _e('The following themes are installed but incomplete.  Themes must have a stylesheet and a template.'); ?></p>

<table width="100%" cellpadding="3" cellspacing="3">
	<tr>
		<th><?php _e('Name'); ?></th>
		<th><?php _e('Description'); ?></th>
	</tr>
<?php
	$theme = '';

	$theme_names = array_keys($broken_themes);
	natcasesort($theme_names);

	foreach ($theme_names as $theme_name) {
		$title = $broken_themes[$theme_name]['Title'];
		$description = $broken_themes[$theme_name]['Description'];

		$theme = ('class="alternate"' == $theme) ? '' : 'class="alternate"';
		echo "
		<tr $theme>
			 <td>$title</td>
			 <td>$description</td>
		</tr>";
	}
?>
</table>
<?php
}
?>

<h2><?php _e('Get More Themes'); ?></h2>
<p><?php _e('You can find additional themes for your site in the <a href="http://wordpress.org/extend/themes/">WordPress theme directory</a>. To install a theme you generally just need to upload the theme folder into your <code>wp-content/themes</code> directory. Once a theme is uploaded, you should see it on this page.'); ?></p>

</div>

<?php require('admin-footer.php'); ?>