Lave sikkerhed, bla mod mysql injection

Har dette script til at logge brugere ind:
if(isset($_GET[login])) {
    $kode = md5($_POST[kodeord]);
    $tjek_login = mysql_query("SELECT id,name FROM users WHERE name = '$_POST[brugernavn]' AND password = '$kode'") or print mysql_error();
    $login = mysql_num_rows($tjek_login);
    $fetch_login=mysql_fetch_array($tjek_login);
    if($login == '1') {
        //LOGIN KORREKT
        session_start();
        $_SESSION['s_id'] = $fetch_login["id"];
        $_SESSION['s_name'] = $fetch_login["name"];
        header("Location: index.php");
    } else {
        //LOGIN FORKERT
        echo"<script>alert(\"Forkert Bruger/Kode, Prøv igen!\");</script>";
    }
}