I am having the exact issues here. I was able to deploy all Win7 images via SCCM/OSD sucessfully upto model Dell Opt 780. When I got to deploy Dell Opt790 using the same boot disk from prev models, I got the same error of Nic driver unavailable. I downloaded all drivers for 790 and created the driver packages for this model but I do not know how to update/inject the new drivers into the existing boot.wim file, please help.