Intranet,not Ethernet

Anyone knows how to create an intranet,good links etc.?
I'm not talking of ethernet connections,I'm asking about connecting many computers together via modem to a central server.
Thanks.

This would require you to have many phone lines hooked in to the central server. Each client computer would need to dial in to a seperate phone number. (At least to my understanding... I'm sure there are other (easier) ways I don't know about.)

Hyperterminal is a windows program which could do this. Connect to the modem. Dial the number with command 'ATDT 5551234'. I'm not sure what the receiving computer's command is, but it's something like 'ATZ'. Hopefully, they'll connect properly. From there you can send text and files to the other computers.

I don't know how to do this in C/C++.

To do this well you need get with your telephone company and have some good resources.

Basically its the same thing as ygfperson described but instead of multiple phone lines you can do this:

Have a DS-1 ran to your building. At your building you need to have a MUX/DEMUX and from there run it to your server.

Each DS-1 can handle 24 lines (there are a few other methods that change that number slightly).

Creating a VPN (virtual private network) over phone line is costly. Not something that a group of friends would be able to easily pull off.