Transfer files between computers

We need to transfer a file from a central computer(Windows XP) to multiple 'branch' computers(WindowsNT/Windows2000) on a weekly basis. This transfer should be done programmatically in C#, when a user clicks a button or a menu item. After the transfer, we need to run a Script/batch file on each client computers. The problem is none of these computers are connected to the internet, but they have modems and can connect to telephone lines. We could do this manually using Hyper Terminal, but we want to program this in C#. We prefer a solution that doesn't make use of internet. Solutions using Hyper Termial APIs too are welcome.The solution we are looking at is something similar to what Hyper Terminal performs - Far away computers connected via Telephone lines. We cant use cables Thanks for your help