Try this:
#!/usr/bin/perl -w
use strict;
use LWP::UserAgent;
use URI::URL;
my $ua = new LWP::UserAgent;
my $page = "http://lsa.colorado.edu/cgi-bin/LSA-sentence-x.html";
my $uri = new URI::URL;
$uri->query_form("LSAspace" => "General_Reading_up_to_1st_year_college
+ (300 factors)",
"LSAFactors" => "",
"txt1" => "I hate Jimmy. I love Jimmy.");
my $req = new HTTP::Request POST => $page;
$req->content_type('application/x-www-form-urlencoded');
$req->content($uri->equery);
my $res = $ua->request($req);
if (!$res->is_success) {
die "Fetch failed\n";
}
my $content = $res->content;
print $content;