This is a generalization of what you'd need to do, in PHP:
><?
ini_set('session.cache_limiter', '');
header('Expires: Thu, 19 Nov 1981 08:52:00 GMT');
header('Cache-Control: must-revalidate, post-check=0, pre-check=0');
header('Pragma: no-cache');
header("Content-Disposition: disposition-type=attachment; filename=XXXa");
readfile("XXXb");
?>
This is a PHP script that you would link to in a page, much like this:
><a href="script.php">Download MP3</a>
This is how I've got things working, more or less. Let me know if it works for you. Replace 'XXXa' with the suggested file save name, and the 'XXXb' with the local (I do believe) path to the file you want them to download.