Process IPN message from Paypal Payments standard?

Hi,

I am wondering what/how I should really do to process IPN message for Paypal Payments Standard regarding to ecart5. Below is a Listener sample code from Paypal. Should I just construct a blank page to include this code?
Should I or how I, modifiy it? If I don't modify it at all, what will happen?
Thanks a lot!

<?php
error_reporting(E_ALL ^ E_NOTICE);
$email = $_GET['ipn_email'];
$header = "";
$emailtext = "";
// Read the post from PayPal and add 'cmd'
$req = 'cmd=_notify-validate';
if(function_exists('get_magic_quotes_gpc'))
{
$get_magic_quotes_exists = true;
}
foreach ($_POST as $key => $value)
// Handle escape characters, which depends on setting of magic quotes
{
if($get_magic_quotes_exists == true && get_magic_quotes_gpc() == 1){
$value = urlencode(stripslashes($value));
} else {
$value = urlencode($value);
}
$req .= "&$key=$value";
}
// Post back to PayPal to validate
$header .= "POST /cgi-bin/webscr HTTP/1.0\r\n";
$header .= "Content-Type: application/x-www-form-urlencoded\r\n";
$header .= "Content-Length: " . strlen($req) . "\r\n\r\n";
$fp = fsockopen ('ssl://www.paypal.com', 443, $errno, $errstr, 30);
// Process validation from PayPal
// TODO: This sample does not test the HTTP response code. All
// HTTP response codes must be handled or you should use an HTTP
// library, such as cUrl
if (!$fp) { // HTTP ERROR
} else {
// NO HTTP ERROR
fputs ($fp, $header . $req);
while (!feof($fp)) {
$res = fgets ($fp, 1024);
if (strcmp ($res, "VERIFIED") == 0) {
// TODO:
// Check the payment_status is Completed
// Check that txn_id has not been previously processed
// Check that receiver_email is your Primary PayPal email
// Check that payment_amount/payment_currency are correct
// Process payment
// If 'VERIFIED', send an email of IPN variables and values to the
// specified email address
foreach ($_POST as $key => $value){
$emailtext .= $key . " = " .$value ."\n\n";
}
mail($email, "Live-VERIFIED IPN", $emailtext . "\n\n" . $req);
} else if (strcmp ($res, "INVALID") == 0) {
// If 'INVALID', send an email. TODO: Log for manual investigation.
foreach ($_POST as $key => $value){
$emailtext .= $key . " = " .$value ."\n\n";
}
mail($email, "Live-INVALID IPN", $emailtext . "\n\n" . $req);
}
}
}
fclose ($fp);
?>