¿Como puedo enviar mensajes por red de Linux a Windows?

De todos modos, en el caso de que estuviera dispuesto a instalar algún programa adicional, en los repos tiene varios para éstos menesteres:

$ urpmq -i kpopup
Name        : kpopup                  
Version     : 0.9.8.1                 
Release     : 1mdk                    
Group       : Graphical desktop/KDE   
Size        : 106378                       Architecture: x86_64
Source RPM  : kpopup-0.9.8.1-1mdk.src.rpm                      
URL         : http://www.henschelsoft.de/                      
Summary     : KDE tool for sending and receiving WinPopup messages
Description :                                                     
This application is a KDE replacement for Microsoft(tm) WinPopup on
Windows. It can send and receive WinPopup messages with Samba.     

This RPM release requires manual user configuration:
Once the package is installed, please add or update this line in
/etc/samba/smb.conf:

  message command = sh -c '/usr/bin/kpopup %s %f' &

$ urpmq -i linpopup
Name        : linpopup
Version     : 2.0.7
Release     : 2mdv2008.1
Group       : Networking/Other
Size        : 344546                       Architecture: x86_64
Source RPM  : linpopup-2.0.7-2mdv2008.1.src.rpm
URL         : http://linpopup2.sourceforge.net/
Summary     : Linux enhanced port of winpopup
Description :
LinPopUp is a Xwindow graphical port of Winpopup,
running over Samba. It permits to communicate with a
windows computer that runs Winpopup, sending or
receiving message. (It also provides an alternative way
to communicate between Linux computers that run Samba).
Please note that LinPopUp is not only a port, as it includes
several enhanced features. Also note that it requires to
have Samba installed to be fully functionnal.

To make this program work you have to add this line to your samba smb.conf
in the [global] section:

message command = /usr/bin/LinPopUp "%f" "%m" %s; rm %s