Código PHP:
<?php
$onlyfile="mi arvhivo del tipo ke sea";
header("Content-type: application/octet-stream\n");
header("Content-Disposition: attachment; filename=\"$onlyfile\"\n");
header("Content-transfer-encoding: binary\n");
header("Content-length: " . filesize("$onlyfile") . "\n");
$fp=fopen("$destino/$onlyfile", "r");
fpassthru($fp);
?>
espero te sirva Salu2