Code:
<?php
$subject = "Check this out!";
$message = "Hey, you should check this out!\r\n" . $_SERVER['HTTP_REFERRER'];
$headers = "From: " . $_POST['from'] . "\r\n" .
"Reply-To: " . $_POST['from'] . "\r\n" .
"X-Mailer: PHP/" . phpversion();
mail($_POST['to'], $subject, $message, $headers);
?>
just make a form with 2 fields in it, 1 with the name from which will be the senders email, and 1 with the name to, which will be who its going to, then put the code above in send.php and link the form to that, you're done.