ищем:
$row = $db->super_query("SELECT subj, text, user_from FROM " . USERPREFIX . "_pm WHERE user = '$member_id[user_id]' AND folder = 'inbox' ORDER BY pm_read ASC, date DESC LIMIT 0,1");
меняем на:
$row = $db->super_query("SELECT subj, text, user_from, id FROM " . USERPREFIX . "_pm WHERE user = '$member_id[user_id]' AND folder = 'inbox' ORDER BY pm_read ASC, date DESC LIMIT 0,1");

ищем:
<div style="width:70%;float:left;padding-left:10px;"><a href="{$PHP_SELF}?do=pm">{$lang['pm_aread']}</a> · <a href='#' onclick="return hs.close(this)">{$lang['pm_close']}</a></div>

меняем на:
<div style="width:90%;float:left;padding-left:10px;"><a href="{$PHP_SELF}?do=pm">Папка входящих</a> :: <a href="{$PHP_SELF}?do=pm&doaction=readpm&pmid={$row['id']}">{$lang['pm_aread']}</a> :: <a href='#' onclick="return hs.close(this)">{$lang['pm_close']}</a></div>

Сохраняем и радуемся =)