use a php script to obscure the file path on the server.
pass the file to be downloaded to a php script. for example:
www.yoursite.com/file_download.php?download_file=test.zip
#######file_download.php#######
<?
$download_folder_path = "/home/downloads/";
$file = $download_folder_path.$download_file;
header ( "Content-Type: application/octet-stream");
header ( "Content-Length: ".filesize($file));
header ( "Content-Disposition: attachment; filename=$download_file");
readfile($file);
###############################
http://www.php.net/manual/en/function.readfile.php