I have several computers running Athlon 64 processors on motherboards with the nVidia nForce 430 chipset which were recently upgraded to Windows 7 x64 from Windows XP64. They each have 4GB RAM, and had either a PRO/1000 MT or PRO/1000 GT NIC to provide gigabit access. Right after upgrading, I noticed that none of the MT or GT adapters could obtain an IP address from the router, even though it all previously worked in the same hardware configuration with XP64, and the onboard 10/100 NICs had no problems connecting to the network. Running updated (Vista) drivers, different PCI slots and swapping with known good cards from other (un-upgraded) computers made no difference; the PRO/1000 MT and GT adapters just couldn't connect. Out of curiosity, I finally pulled 2GB RAM out of one of the systems, and the PRO/1000 adapter worked like a charm!
Now, since the whole point of x64 is to run with over 3GB RAM, I don't want to keep the machines in a gimped configuration. Does anyone know of a fix or a workaround for this issue?