Here's a working start using Win32::API and Win32::API::Callback to handle EnumWindows. Error handling is up to you ;)

use strict;
use warnings;
use Win32::API;
use Win32::API::Callback;

my $getwindowtext = Win32::API->new( 'user32', 'GetWindowText', 'NPN',
+ 'N' );
my $enumwindows = Win32::API->new( 'user32', 'EnumWindows', 'KN', 'N' 
+);

my $title = shift || "Mozilla";
$title = qr/\Q$title\E/i;

my $cb = Win32::API::Callback-> new( 
        sub {
            my $hwnd = shift;
            my $text = " " x 255;
            my $length = $getwindowtext->Call( $hwnd, $text, 255 );
            $text = substr( $text, 0, $length );
            if ( $text =~ $title ) {
                print "$text\n";
            }
            1;
        }, "NN", "N",
    );
my $ret = $enumwindows->Call( $cb, 0 );
[download]

C:\S>perl enumwin.pl Mozilla
Command Prompt - perl enumwin.pl Mozilla
preview page - Mozilla Firefox
[download]