Assuming this is about stealing bandwidth (no way to stop people from saving your flash to their computers), and you're not into the Apache options posted above, this would be a way to serve up a file using CGI:

use strict;
use warnings;
use CGI;

my $flash_file = 'your_flash_file.swf';
open FLASH, '<', $flash_file or die $!;
binmode FLASH;

my $q = new CGI;
print $q->header(
                 -content-type   => 'flash/swf'
                 -content_Length => (stat FLASH)[7]
                );

my $buffer;
while (read(FLASH, $buffer, 1024) > 0){
    print $buffer;
}

close FLASH;
[download]

(add error-checking!)

You may need to do some research on the HTTP headers to send along with the data. I am just guessing at the Content-type, for instance.

Hope this helps.