I too have this problem with NICs. I only seem to run into the problem with 4GB of memory installed in my system. I'm running Windows 7 RTM x64 on both of my machines. If I run 3GB dual channel in these machines I have no problem with the NICs.
How much memory is in your system. I have two Windows 7 RTM machines. When I have 3GB of memory in them they work fine. When I put 4GB in either system my network cards fail to function.