Avoid LAN Spread Virus'

My current situation is I have a 4-port cable modem, a 4-port hub, and a 4-port router. It is currently set up in this configuration...



I work at home as a subcontractor for a company that builds and fixes computers. The extra cable for project PC's is designated to that task. My issue is that a lot of the computers I am fixing are infected with Virus'. I know that some well programmed virus' can be spread through a LAN. The most obvious solution to this problem is to not connect the project PC to the network until all virus' are removed, but sometimes this is hard to avoid. My question is will keeping the project PC outside my router help protect the PC's inside the router from LAN spread virus'?