Just run an ethernet cable between them. Most modern computers have auto-sensing MIDX ethernet ports, so you can use a standard ethernet cable and they will automatically set the polarity correctly. And if the computers are configured to use DHCP (which is usually the default), they will automatically configure themselves using the 169.254.x.x network. Just make sure each is using the same Windows workgroup name and sharing a common username/password for authorizing access to shared resources.