You don't need a router. If you set the subnet mask on all of the PCs to be 255.255.0.0, then they should all be able to ping each other. Basically, opening up the subnet mask puts all of the PCs on ...
At home I have two computers, in two different rooms, both with internet access. My main computer is connected through a router that is connected to a cable modem, the cable modem is also connected to ...