[Adrian Schneider]

There are several ways you can do it. The easiest is

PHP Code:

if (!empty($vbulletin->templatecache['template_name']))
{
    // template exists and is cached
} 


if it's not cached, then... you could use a query

PHP Code:

if ($vbulletin->db->query_first("
    SELECT templateid
    FROM " . TABLE_PREFIX . "template
    WHERE title = 'template_name'
"))
{
    // template exists
}