That will only work if the computers are on the same physical network, but why on earth would anyone use different IP subnets and IP ranges on the same physical network? Which actually gets back to his original question which I never completely answered either. A router is completely capable of routing the two network addresses, but Microsoft networks rely on a lot of other (let's call them sub protocols) for its services to function. So TCP/IP connectivity isn't enough. That's why you can't just browse files across the Internet. To have a fully functioning MS network like this you need some sort of VPN tunnel. The VPN tunnel then encapsulates all the other protocols in TCP packets and sends them each way, basically "bridging" the two desparet networks.