in effetti mi sa che non ci avevo capito un ca**o 
questo dovrebbe andare meglio.... l'ho postato giorni fa nel forum
codice:
$file = "download/".$DownFile;
if (!is_file($file)) { die("404 File not found!"); }
$file_extension = strtolower(substr(strrchr($filename,"."),1));
switch( $file_extension ) {
case "pdf": $ctype="application/pdf"; break;
case "exe": $ctype="application/octet-stream"; break;
case "zip": $ctype="application/zip"; break;
case "doc": $ctype="application/msword"; break;
case "xls": $ctype="application/vnd.ms-excel"; break;
case "ppt": $ctype="application/vnd.ms-powerpoint"; break;
case "gif": $ctype="image/gif"; break;
case "png": $ctype="image/png"; break;
case "jpeg":
case "jpg": $ctype="image/jpg"; break;
case "mp3": $ctype="audio/mpeg"; break;
case "wav": $ctype="audio/x-wav"; break;
case "mpeg":
case "mpg":
case "mpe": $ctype="video/mpeg"; break;
case "mov": $ctype="video/quicktime"; break;
case "avi": $ctype="video/x-msvideo"; break;
case "php":
case "htm":
case "html":
case "txt": die("Cannot be used for ". $file_extension ." files!"); break;
default: $ctype="application/force-download";
header("Content-Description: File Transfer");
header("Content-Type: application/force-download");
header("Content-Type: $ctype", FALSE);
header("Content-Type: application/download", FALSE);
header("Content-Disposition: attachment; filename=".basename($file));
header("Content-Transfer-Encoding: binary");
header("Content-Length: ".filesize($file));
readfile("$file");