I had a look at the HTML source of the racing results page. The following fragment defines the post action ...

<form action=monthresultslist.asp method=post> ...
[download]

As you can see here, you are posting to the wrong URL.

However, you could use WWW::Mechanize to do the browsing for you...

#!/usr/bin/perl -w
use strict;
use WWW::Mechanize;

my $url = 'http://www.gulfgreyhound.com/officialracingresults.asp';

my $robot = new WWW::Mechanize;
$robot->get($url);
$robot->form_number('1');
$robot->set_fields('subfolder' => 'dec03');
$robot->click();

# Get the reply to my question
my $html = $robot->content();

print "$html";
[download]