testdatei.txt 

<?PHP
if (file_exists($path . $_GET['file']))
$path = "F:\\www\\";
header("Content-type: application/octet-stream\n");
header("Content-disposition: attachment; filename=\"" . $_GET['file'] . "\"\n");
header("Content-transfer-encoding: binary\n");
header("Content-length: " . filesize($path . $_GET['file']) . "\n");
$fp = fopen($path . $_GET['file'], "r");
fpassthru($fp); 
fclose ($fp);
} else
echo "datei existiert nicht";