Hello!
I tried the code from the original post on Windows XP, ActivePerl 5.8.7 Build 815 with a Garmin GPS 12CX attached to COM4 and it didn't work.
No worries though.
So... I put together a variation of the original post using GPS::Garmin which is a subset module to perl::GPS
I have posted the "new code" below.
++ to the original author for inspiring me to dig further and find this module to interface with my Garmin! Yet Another Cool Use For Perl!
Important Note: Garmin::GPS on Win32 wants to see installed Win32::SerialPort, however, ActiveState does not appear to offer it for perl 5.8 and above. I did a little digging and installed it directly via the ppm prompt by issuing the command

ppm>install http://www.bribes.org/perl/ppm/Win32-SerialPort.ppd
[download]

With that little problem solved the script below works quite well.

#!/usr/bin/perl
use warnings;
use strict;
use Tk;
use GPS::Garmin; 
use Win32::SerialPort;


my $mw = MainWindow->new;


$mw->withdraw;

my $location;

my $gps = new GPS::Garmin( 'Port' => 'COM4', 'Baud' => 9600, );
my ($latsign,$lat,$lonsign,$lon) = $gps->get_position;
my ($sec,$min,$hour,$mday,$mon,$year) = $gps->get_time;
my $time="$hour:$min:$sec";
$lat=sprintf("%.4f",$lat);
$lon=sprintf("%.4f",$lon);

$location="$lat$latsign $lon$lonsign";
my $locationandtime="$lat$latsign $lon$lonsign\n$time"." GMT";

$mw->messageBox (
    -message => $locationandtime, -title => 'Time and location', -type
+ => 'Ok'
    );
[download]

I am thinking more possibilities for tinkering there will soon be! :)