Actually, there IS the problem. After clicking on 'Download' button the _zero_ file 'download.php' will be sent by PHP script. In web browsers other than IE the situation may be even worser. The only solution is, step-by-step: 1) use only IE; 2) after clicking 'Download' the standart IE download window will appear. Choose 'Open from location' (DO NOT save this file); 3) on the next SAME-LOOKING (but not the same - check what the server is trying to download to you now) window do the same as in step 2; 4) and only the next window wil hold the link you need - choose ' Save on disk' and hold your breath when IE loads the file.
IMHO, php-script is buggy.