Well your hurdle is going to be the refresh of the UI files. I am working on a work around for that right now. As for the rest, its easy.
Take a look at my bag code for a working example. First you would have your go between program edit the settings file. All it would need to do is put a data source saying something like.
Code:
person.talking="fred"
and when no one is talking say
Code:
person.talking="false"
Next you need to have the eq2 UI reload, that's the hurdle.
Next you would use conditional statments in each window
Code:
showicon.visible=(person.talking)'=='(groupmember1.playername)
if the names are the same (you would have to have your go between match the names) then the icon will show. If not it will not.
You can add an effector in there to play a sound or even just show the icon for a few seconds. see how I used the randomness page with a 1 second delay to execute code 1 second after I told the program to execute it.
you could also have it activate a button that has more complex code in it, such as re arrangment of the windows and such, sky is the limit.
As for the current hurdle, I have a few ideas, this weekend i'll be disecting mother's mail window that can include text from a text file. Also the mail window and friends window alters none xml text, may be able to work around with that as well.