Sending "pop up" messages to peer machines

[Don Russell]

I have an FC7 box running some basic things like e-mail etc.

The LAN is basicaly made up of that machine and a handful of Windows 
(2000 and XP) machines.
I am also anticipating adding an Apple Mac machine to the mix, as well 
as a Linux laptop.

I want an application on the FC7 box to send a "pop up" message to all 
the other machines on the network.

In researching "net send <bios-name> <text>" I discovered a program like 
WinPopup is needed on the windows machines... further investigation into 
that looks like it's old information, pertaining to Windows 3.1, 95 and 
98, explicitly NOT supported in Windows NT... and I'm assuming Windows 
2000/XP.

The question is... how do I make my FC7 box "aware" of all the other 
machines on the peer network so it knows who to send messages to?

Is there some sort of broadcast I can send out like a "OK, sound 
off...." and all recipients of that broadcast respond with a "OK, my 
name is ..." (or just having the IP address would probably suffice)

Then I can send the message to each device that replied...

Anybody have any pointers/suggestions?

Thank you