Without using a VPN and without using a router. The OS Windows 7 Ultimate on the systems used as the "server". Is there a way to map a drive letter on another remote system running windows 7 Premium to connect to the "server" system solely on the basis of the IP address. The IP is a static address which would be programmed into the IPV4 address settings along withthe gateway and DNS into the NIC on the system acting as the "server". Basically these are the same settings that would normally have gone into the router for the Incoming WAN.
This would be the only system on that IP. The shared folders would be done using windows file sharing and permissions. And any connections would be challenged for this information before allowing the connection.
Can this be done? If so, how could it be made as secure as possible?