If you can find a 'small enough' mini-ITX case with a half-height PCI slot, then it's easy: socket 1155 Motherboard with 1 Intel NIC (Gigabyte or AsRock or Jetway) Haswell CPU RAM Half-height dual-port PCIe Intel NIC (should be under $150, maybe less)
If you need something smaller than that, it gets much more expensive. There's some pre-built systems, or there's a couple mini-ITX boards such as this one: AnandTech | GIGABYTE Server Launches New C2750 Mini-ITX and 2P ATX LGA2011 However, I would be wary of the Atom CPUs unless you don't have a high-bandwidth connection.
Supermicro and others make small rackmount boards/systems with faster CPUs, but they're going to be very noisy.
If you can find a 'small enough' mini-ITX case with a half-height PCI slot, then it's easy: socket 1155 Motherboard with 1 Intel NIC (Gigabyte or AsRock or Jetway) Haswell CPU RAM Half-height dual-port PCIe Intel NIC (should be under $150, maybe less)
If you need something smaller than that, it gets much more expensive. There's some pre-built systems, or there's a couple mini-ITX boards such as this one: AnandTech | GIGABYTE Server Launches New C2750 Mini-ITX and 2P ATX LGA2011 However, I would be wary of the Atom CPUs unless you don't have a high-bandwidth connection.
Supermicro and others make small rackmount boards/systems with faster CPUs, but they're going to be very noisy.
