Barrage Of Questions...Theory impossible? File IO on Web Domain?

In my quest to finish this interface by the deadline my staff gave me, Christmas. I had chosen Visual C++ as the language of choice for this. MAny of you agreed and gave me highly essential aid in my learning this language.
I have learned quite a bit now. And relize its nearly exactly like another language I knew, which helped a lot, but then I turn to VC which is far unlike anything ive ever played with save VB and VB was just a pain. So I have a few questions for you, my friends.


In my interface, Im developing a chatroom and a messenger service that runs locally on your harddrive and connects through the website.
The logic in the way it should worked seems possible, and from what I am told, it is.
The chatroom is too function like so : basically noone directly connects to one another, everyone is simply looking at the same text file on the website. And whenever it is changed, a variable is changed in a users file that is checked consistantly and the chat.txt is slapped onto the user's window and updated, giving the apperance of a real time chatroom.
SAme thing with the messenger service, simply that if a message is left in the users txt file a dialog box will be slapped at them giving them the message.

Windows, box, message thingies, no problem. The problem I am having, is simply this. How do I do IO with several users on my web domain? As in reading and altering the file on-site? A Safe and secure way? someone suggested a script talking to the users program but thats beyond what I know. I simply need an idea or thesis on how to execute the logic seen above. Any aid my friends? Theres miller light and tostidos in it for anyone who gives me a hand. :-)

Sincerly,
The Lord Of The Arches
Zedd