Consider creating a virtual private network (VPN). It uses the internet to network computers that are distant from each other.
You don't need to connect them by ethernet cables as with a local area network. Each computer in the network accesses its own internet provider the normal way. Then it locates your VPN and hooks up to it by a password.
VPN may be an option in your network settings, or it may require the server version of Windows. My Mac running OSX has category for it. However I don't see it as a choice in the Win XP network wizard on my Compaq.
Can't supply any more info than the above.