I was running into problems trying to get the zip file to download. I was getting the prompt to download, but the file was coming up empty. The problem I was running into was that the connection to the browser is a stateless connection, and lost the credentials that was being used in getting the file in the first step. Had to save the file locally to a temp directory and create a direct link, (files are deleted after 24 hours) allowing people to download the file directly. This is what I ended up doing:

$filename = 'test.zip';

# get file from external ftp
use LWP::UserAgent; 
use HTTP::Request::Common;
my $url = "http://www.domain.com/$filename"; 
my $ua = LWP::UserAgent->new(keep_alive=>1); 
my $headers = HTTP::Headers->new(); 
$headers->authorization_basic('user', 'pass'); 
my $request = new HTTP::Request(GET => $url, $headers); 
my $response = $ua->request($request);
print "response:" . $response->code . "<br>";

# save file locally
$filepath = "e:/myfolder/Data/$filename";
open(ZIP, ">$filepath");
binmode ZIP;
print ZIP $response->content;
close(ZIP);

# provide link to download file
print "Download file <a href="http://www.localftp.com/Data/$filename">
+here</a>";
[download]

Don't think there was a solution to downloading the file via the a prompt.