[kh99]

There is a table called postparsed that caches the html for a post. It's done separately for each style and language, so you would really need to check postid, styleid, and languageid to see if a given postid is cached for the current value of STYLEID and LANGUAGEID. So maybe something like:

$cached = $vbulletin->db->query_first("
                SELECT * FROM " . TABLE_PREFIX . "postparsed 
                WHERE postid = $postid 
                AND styleid = " . intval(STYLEID) . "
                AND languageid = " . intval(LANGUAGEID) . "
                                ");
if ($cached) 
{
   /// post is cached
}