I've had no issues streaming three concurrent HD (mix of 1080i and 720p) streams from my NAS with it's single on-board Gb NIC.
Unless you get the dual Gb NIC at basically the same price as a decent Intel PROSet Gb NIC I wouldn't bother.
Unless you get the dual Gb NIC at basically the same price as a decent Intel PROSet Gb NIC I wouldn't bother.