Sbaglio mio, prova cosi

invia.php:
<form name="action" action="ricevi.php? id='.$id.'" method="POST">

<?php print '
<input type="text" size="1" maxlength="20" name="id" value="'.$id.'"/> '
?>
<input type="submit" name="action" value="invia" /></form>


ricevi.php

<?php
$id=$_POST['id'];
echo "$id";
?>