$weekly = mktime (date("H"), date("i"), date("s"), date("m"), date("d")-7, date("Y"));
$monthly = mktime (date("H"), date("i"), date("s"), date("m")-1, date("d"), date("Y"));
$new_userW=$DB_site->query_first("SELECT count(*) as count FROM user WHERE joindate>$weekly");
$weeklyuser=$new_userW['count'];
$new_userM=$DB_site->query_first("SELECT count(*) as count FROM user WHERE joindate>$monthly");
$monthlyuser=$new_userM['count'];
Now use variables $monthlyuser and $weeklyuser in the relevant template or your code..