PHP Code:
<?php
if (isset ($_POST['submit'])) {
$username = $_POST['username'];
$password = $_POST['password'];
if ($username == 'user' && $password == 'pass') {
echo 'logged in';
} else {
echo 'Incorrect username/password!';
}
} else {
echo '<form action="index.php" method="post">
Username: <input type="text" name="username" /><br />
Password: <input type="password" name="password" /><br />
<input type="submit" name="submit" value="Login" />
</form>';
}
?>
Change 'user' and 'pass' to whatever you want.
Extremely simple version.