<?php
if ($_SESSION["loggedin"]){
header("Location: home.php");
}
else {
?>

<form method="POST" action="login.php">
    <div align="center">
        Username: <input type="text" name="username" size="15" /><br />
        Password: <input type="password" name="password" size="15" /><br />
        <p><input type="submit" value="Login" /></p>
    </div>
</form>
<?php
}
?>