[NTLDR]

Basing it on X Posts in X time wouldn't be very efficent, especially if you have alot of members and alot of posts. Basing it on say total posts and the last activity is easily doable though (replacing X with the total posts) this would get all users with X posts that have visted in the past week:

PHP Code:

$members = $DB_site->query_first("SELECT COUNT(*) AS users FROM " . TABLE_PREFIX . "user WHERE posts >= X AND lastactivity >= ".TIMENOW - (60 * 60 * 24 * 7));