When choosing a motherboard, check that the ethernet controller is using either the pci-x or pci-e bus.
Intel: http://www.intel.com/design/network/products/ethernet/linecard_ec.htm
Broadcom: http://www.broadcom.com/products/Enterprise-Small-Office/Gigabit-Ethernet-Controllers
Realtek: http://www.realtek.com.tw/products/products1-1.aspx?lineid=1