I need to develop a app that in some manner reads/displays a message

Sort of like a broadcast netsend

I have about 1500-2000 machines in 10 different sites, both XP and win7

This is to alert staff when things like the mailserver goes off-line or we need to send an immediate message to all staff.

I was considering a client app that monitored a network folder waiting for a file containing a message to appear. The client would read the file and popup a kixform displaying the message.

The problem as I see it is the traffic of having all these PCs monitoring that folder.

The second method I thought of was to copy that file to every PC that is online, and the client app monitors a local folder for a message file to appear.. but that could take quite a while sending a file across the WAN to every PC.

A 3rd method was a distributed sort of thing where each IP subnet monitored a folder in their subnet, and the message sender would copy to the folder in every subnet (instead of every PC)

Any better ideas?
_________________________
How to ask questions the smart way <-----------> Before you ask