и още една оптимизациика :
$Selstr="select * from user where user='".addslashes($user_id)."' and password='".addslashes($password)."'";
$Selstr="select count(*) from user where user='".addslashes($user_id)."' and password='".addslashes($password)."'";
и после проверяваш колко е каунта :-))))

root@localhost#cd /pub
root@localhost#more beer