Read docs for HTTP::Request::Common. You should have something like (untested):

use HTTP::Request::Common;
use LWP;
my $ua = LWP::UserAgent->new;
my $res = $ua->request(POST 'http://server.com/cgi-bin/upload.cgi',
    Content_Type => 'form-data',
    Content => [ description => 'a description', 
                 filetoupload => ['c:/test.dat'] ]);
....
....
[download]

Note that you probably do not need to use CGI if you want to write HTTP client.

--
Ilya Martynov (http://martynov.org/)