What is the best way to configure our machine with two ethernet jacks; one to connect the server to the internet, and the other to connect to the switch that runs to the rest of the machines? If the motherboard already has a gigabit ethernet port, can we install a PCI network interface card and assign each device to a different task? Or would it be better to buy a dual-port card such as this one?
I don't think I would run the wan throught the server. Just plug the router into the switch with everything else. The 2 ethernet ports are better served by trunking them to the switch. You can alway control internet access by policy.