Here's a working example...

use Win32;
use Win32::GuiTest qw(:ALL);
    
my $searchString = 'Internet Explorer';
    
for (FindWindowLike()) {        
    my $title = GetWindowText($_);    
    next unless ( $title );
    if( $title =~ /$searchString/ )  { 
        print "$title\n"; 
    }
}
[download]

Update: Added code example that applies to Internet Explorer