You need to be careful how you do this as Tk will block and you will not be able to access any other functionality of your Tk program until the called program exits. This may not be an issue unless the called program takes a long time to execute.

Also can I run a "EXE" program?

This leads me to believe you are doing this in a Windows environment. Check out Win32::Process for how to call an "EXE" as a subprocess (which will prevent blocking). The code below is a very simple example of what you are probably looking for.

use Tk;
use Win32::Process;
use Win32;

use strict;

my $mw = MainWindow->new();
my $npBtn = $mw->Button(-text => "Notepad", 
                        -command => [\&run_prog, "C:\\winnt\\system32\
+\notepad.exe"]
                       )->pack();

my $cBtn = $mw->Button(-text => "Calc", 
                       -command => [\&run_prog, "C:\\winnt\\system32\\
+calc.exe"]
                      )->pack();

MainLoop;

sub run_prog() {
    my $prog = shift;
    Win32::Process::Create($po, 
                           $prog, 
                           "",
                           0, 
                           NORMAL_PRIORITY_CLASS, "."
                          ) || die &error();
}

sub error() {
    print Win32::FormatMessage( Win32::GetLastError() );
}
[download]

hope this helps,
davidj