Skrypt logowania i rejstracji uzytkownikow - problem Opcje

[stal-sw]

Ponizej mam skrypt ktory wykonuje formularz logowania (login, password).
Jednak nie wiem jak zabezpieczyc np. wszystkie skrypty na stronie - aby nikt nie zalogowany - nie mogl go uruchomic.

Tzn jaki kod wstawic przed kazdym skryptem, aby go nie mozna bylo uruchomic jesli sie nie jest zalogowanym na stronie?

[php:1:be26129778]
<?
/* Check User Script */
session_start(); // Start Session

include 'db.php';
// Conver to simple variables
$username = $_POST['username'];
$password = $_POST['password'];

if((!$username) || (!$password)){
echo "Please enter ALL of the information! <br />";
include 'login_form.html';
exit();
}

// Convert password to md5 hash
$password = md5($password);

// check if the user info validates the db
$sql = mysql_query("SELECT * FROM users WHERE username='$username' AND password='$password' AND activated='1'");
$login_check = mysql_num_rows($sql);

if($login_check > 0){
while($row = mysql_fetch_array($sql)){
foreach( $row AS $key => $val ){
$$key = stripslashes( $val );
}
// Register some session variables!
session_register('first_name');
$_SESSION['first_name'] = $first_name;
session_register('last_name');
$_SESSION['last_name'] = $last_name;
session_register('email_address');
$_SESSION['email_address'] = $email_address;
session_register('special_user');
$_SESSION['user_level'] = $user_level;

mysql_query("UPDATE users SET last_login=now() WHERE userid='$userid'");

header("Location: login_success.php");
}
} else {
echo "You could not be logged in! Either the username and password do not match or you have not validated your membership!<br />
Please try again!<br />";
include 'login_form.html';
}
?>[/php:1:be26129778]

[Nitro]

Można np. tak:
[php:1:84f354d856]<?php
session_start( );
if( session_is_registered( 'username' ) ) {
echo( 'OK' );
}
else {
echo( 'Zaloguj się...' )
}
?>[/php:1:84f354d856]
poza tym, nie jest końeczne stosowanie obu tych metod:
[php:1:84f354d856]
session_register('first_name');
$_SESSION['first_name'] = $first_name;
[/php:1:84f354d856]
wystarczy jedena z nich, raczej ta druga.