You need to replace your hub with a switch, and the other 3 computers should also be on a switch instead of a router, technically speaking. There is only a need for a router at the ingress point to your LAN from the internet, to be used as a gateway. A switch is better suited to handle full duplex traffic from multiple hosts than is a router. With that many computers on a home network, I would recommend getting two gigabit switches and CAT6 cable if you can afford it.