Best way to do a login? [Advice Needed, Not Help]

[Seraphino]

Hi, I have been working on one of my more harder PHP applications for the last few weeks and I am nearing the finality of it and it is almost ready to be handed over to the people I am developing it for. However, I wanted to make sure that I was doing my login script to the best of security and speed.

Any advice would be nice as I do want this to make great turnout for me.

(PS: The MYSQL_SERVER caps is not a bleep, those are defines in the config file)

<?
include('includes/config.php');
$r_username = $_POST['username'];
$r_password = $_POST['password'];

if (!mysql_connect(MYSQL_SERVER, MYSQL_USERNAME, MYSQL_PASSWORD))
{
    echo "Error connecting to mysql server!";
}
else
{
    mysql_select_db(MYSQL_DATABASE);
}

$query = sprintf("SELECT * FROM Users WHERE Username='$r_username' AND ASCII(Password='$r_password')", mysql_real_escape_string($r_username),
mysql_real_escape_string($r_password));

$result = mysql_query($query);
if (!$result)
{
    $num = "This Username or Password is Invalid";
}
else
{
    $num = mysql_num_rows($result);
}


if ($num == "This Username or Password is Invalid")
{
    echo "Error! You can not proceed with an invalid account!";
}
elseif($num != 0)
{
    if (MAINTENANCE == true)
    {
        if ($r_username == ROOT_USERNAME and $r_password == ROOT_PASSWORD)
        {
            setcookie("admin_MMM", "true");
            setcookie("account", $r_username);
            setcookie("account_password", $r_password);
            setcookie("MECHNET_LOGGED_IN", "true");

            echo "Welcome back Administrator $r_username! Redirecting...";
            ?>
            <script type="text/javascript">
            <!--
            setTimeout("location.href='<? echo MODEL_URL; ?>'",5000)
            //-->
            </script>
            <?
        }
        else
        {
            echo "Error, the application is currently in MAINTENANCE MODE, non-admins are not allowed to login at this time";
        }
    }
    else
    {
        if ($r_username == ROOT_USERNAME and $r_password == ROOT_PASSWORD)
        {
            setcookie("admin_MMM", "false");
            setcookie("account", $r_username);
            setcookie("account_password", $r_password);
            setcookie("MECHNET_LOGGED_IN", "true");

            echo "Welcome back Administrator $r_username! Redirecting...";
            ?>
            <script type="text/javascript">
            <!--
            setTimeout("location.href='<? echo MODEL_URL; ?>'",5000)
            //-->
            </script>
            <?
        }
        else
        {
            setcookie("admin", false);
            setcookie("account", $r_username);
            setcookie("account_password", $r_password);
    
            echo "Welcome back $r_username, redirecting...";
            ?>
            <script type="text/javascript">
            <!--
            setTimeout("location.href='<? echo MODEL_URL; ?>'",5000);
            //-->
            </script>
            <?
        }
    }
}
else
{
    echo "There was an error in accessing account information";
}


?>