index.php?x=blahblah.mp3

You'll need a database with at least two tables (name and url)
then use something like this code to generate a list of all the rows (entries) in that database.

PHP Code:

<?
$sql = mysql_query("SELECT * FROM database ") or die (mysql_error());

while ($row = mysql_fetch_array($sql)) {
$name = $row["name"];
$url = $row["url"];

echo "<a href=\"folder/$url.mp3\">$name</a><br />";

}

?>

I think that should work, but I'm still kinda new to php coding.