Disable theme switching

Paste the following code into functions.php

add_action('admin_init', 'slt_lock_theme');
function slt_lock_theme() {
 global $submenu, $userdata;
 get_currentuserinfo();
 if ($userdata->ID != 1) {
  unset($submenu['themes.php'][5]);
  unset($submenu['themes.php'][15]);
 }
}