This is a hack, but seems to work on linux. I noted 2 needed (but weird) focus calls, that I found by experimenting. :-)

#!/usr/bin/perl
use strict;
use warnings;
use Tk;
use Tk::Entry;

my $mw = new MainWindow;

my $warning = 'alphanumeric entered';
   
my $tl = $mw->Toplevel();             
$tl->geometry('300x100+300+300');                                     
+       
my $wlabel= $tl->Label(-textvariable => \$warning)
     ->pack(-expand=>1,-fill=>'both');
$tl->withdraw;

my $new_label = $mw -> Label(-text=>"Enter any character",
    -foreground=>"red",
)-> pack(-side=>"top");

my $ent=$mw->Entry()->pack();

my $press = $mw -> Button(-text=>"Show Me",
       -command =>\&PressMe,
          )-> pack(-side=>"left",-padx=>"5", -ipadx=>"5");


$mw->bind( '<FocusOut>' => sub{ 
            $tl->withdraw; 
            $mw->focus;  #hack needed to prevent recursion
            } );

$mw->bind( '<FocusIn>' => \&PressMe );

MainLoop;

sub PressMe{
    my $val = $ent->get();

 if ($val =~ m/[a-zA-Z0-9]/) {
      $tl->deiconify; 
      $tl->raise; 
      $ent->focus;   #hack needed to prevent recursion
     }
    return;
}
[download]

thanks zentara..but somehow it is not working.. well I have done something to get around of this problem... But now my problem is that i am not able to get the same error/info/warning icons as i was getting using MessageBox widget.Only simple perl built-in bitmaps, i am able to get. Please help if anybody knows how to get those icons.

use strict;
use warnings;

use Tk;
use Tk::Entry;

our $mw = new MainWindow;
our $main;

my $new_label = $mw -> Label(-text=>"Enter any character",
    -foreground=>"red",
    -font => "verdanafont 10 bold") 
-> pack(-side=>"top");

my $ent=$mw->Entry()->pack();
my $press = $mw -> Button(-text=>"Press Me",
    -command =>\&PressMe,
    -font => "verdanafont 10 bold")
-> pack(-side=>"left",-padx=>"5",
    -ipadx=>"5");


MainLoop;

sub PressMe
{
    
            
                my $val = $ent->get();
        if ($val =~ m/[a-zA-Z0-9]/)
        {
            #my $response=$mw -> messageBox(-type=>"ok", -message=>"al
+phanumeric entered",-icon=>"info",-title=> "info!!");
        if (!Exists($main))
            {
            $main = $mw->Toplevel;
            $main->geometry("250x100");
            $main->transient($mw);
            $main->protocol('WM_DELETE_WINDOW' => sub {$main->destroy(
+);});
            #$main->Photo('-format'=>'jpeg', -file => "\@C:\\warn.jpg"
+);
            #my $l=$main->Label(-image=>'hi')->pack;
            my $l = $main->Label(-bitmap=>"info")->pack(-side=>"left")
+;
            my $ll=$main->Label(-text=>"Alpha numeric entered !")->pac
+k();
            }
            else
            {
            $main->deiconify();
            $main->raise();
            } 
        }
    return;
}
[download]

Make your own icons or graphics. See zicons-Tk-Icon-Selector. When you want to start making custom code, you need to do alot of things yourself.

---

I'm not really a human, but I play one on earth Remember How Lucky You Are

thanks for giving your inputs... since i am new to Perl/tk i dont know how to create new widget. Thats why i am looking for work arounds, suggest me if you have any