А вот файл email_pass_check.php
include 'db.php';
if (isset($_POST['email']))
{
$res = mysql_query("select * from users where email = '".mysql_real_escape_string($_POST['email'])."' and is_active = 1");
if (mysql_num_rows($res) > 0)
{
echo 1;
} else {
echo 0;
}
}