de:
<?php

ob_start();
session_start();

require_once ("functions.php");

$returnurl = urlencode(isset($_GET["returnurl"])?$_GET["returnurl"]:"");
if($returnurl == "")
    $returnurl = urlencode(isset($_POST["returnurl"])?$_POST["returnurl"]:"");

$do = isset($_GET["do"])?$_GET["do"]:"";

$do = strtolower($do);

switch($do)
{
case "":
    if (checkLoggedin())
    {
        echo "<H1>You are already logged in - <A href = \"login.php?do=logout\">logout</A></h1>";
    }
    else
    {
        ?>
        <form NAME="login1" ACTION="login.php?do=login" METHOD="POST" ONSUBMIT="return aValidator();">
        <input TYPE="hidden" name="returnurl" value="<?$returnurl?>">
        <TABLE cellspacing="3">
        <TR>
            <TD>Username:</TD>
            <TD><input TYPE="TEXT" NAME="username"></TD>
            <TD>Password:</TD>
            <TD><input TYPE="PASSWORD" NAME="password"></TD>
        </TR>
        <TR>
            <TD colspan="4" ALIGN="center"><input TYPE="CHECKBOX" NAME="remme">&nbsp;Remember me for the next time I visit</TD>
        </TR>
        <TR>
            <TD ALIGN="CENTER" COLSPAN="4"><input TYPE="SUBMIT" name="submit" value="Login"></TD>
        </TR>
        </form>
        </TABLE>
    <?
    }
    break;
case "login":
    $username = isset($_POST["username"])?$_POST["username"]:"";
    $password = isset($_POST["password"])?$_POST["password"]:"";

    if ($username=="" or $password=="" )
    {
        echo "<h1>Username or password is blank</h1>";
        clearsessionscookies();
        header("location: login.php?returnurl=$returnurl");
    }
    else
    {
        if(confirmuser($username,md5($password))) // As pointed out by asgard2005
        {
            createsessions($username,$password);
            if ($returnurl<>"")
                header("location: $returnurl");
            else
            {
                header("Location: index.php");
            }
        }
        else
        {
            echo "<h1>Invalid Username and/Or password</h1>";
            clearsessionscookies();
            header("location: login.php?returnurl=$returnurl");
        }
    }
    break;
case "logout":
    clearsessionscookies();
    header("location: index.php");
    break;
}
?>