You could do this the way chromatic suggested, with a persistent array.
Another way to do it would be with the hidden input type.

However, looking at what you're trying to do here, there's really no need for state maintenance.
Therefore, all you'd need to do is to log all the input you get to a file (a flat text file would do if you're not expecting it to get big), or to a database (which can then do all the sorting for you).
The flat text file approach would involve the use of something like:

use CGI;
open (DB, "data") || die "$!";
$cgi_object = new CGI(DB);
[download]

and the database one will depend on DBI.pm and the relevant DBD module.
Is the above what you are actually trying to do, or this an XYZ question?

setantae@eidosnet.co.uk|setantae|www.setantae.uklinux.net