Yes you need a Network driver - you will not find a WHS2011 version so use Windows Server 2008 R2 drivers. The Fujitsu site lists 3 potential network chipsets for your server - find which you have and use the 64-bit R2 drivers for it. Failing that use each
of the 3 above until one works.
Phil P.S. If you find my comment helpful or if it answers your question, please mark it as such.