Great, both of you are great, Now I am doing something like this:

use strict;

use Tk;
use Tk::DialogBox;

my $mw = new MainWindow();
my $dialog = $mw->DialogBox(-title => "Login",
                            -buttons => ["OK", "Cancel"]);
my $id = $dialog->add("Entry")
                ->pack();
my $passwd;
my $password = $dialog->add("Entry",
                            -show => "*",
                            -textvariable => \$passwd)
                      ->pack();
if ($dialog->Show() eq "OK") {
    print $passwd, "\n";#this line is only for demo
} 

MainLoop;
[download]

I always use Text(height => 1) for one-line entries, and now I realize that for lots of those places, actually I should use Entry instead. Thanks again, have a great day.