realtek has just released new drivers for their ethernet products.
i had the ugly "ethernet-connection-drop" -problem all the time with my Windows 7-builds, even with the rtm.
now i installed the new driver today and until now all runs fine without errors.
i didnt even touch the default configuration of the ethernet card!
i am very happy with that, because the random drop of the ethernet connection is a great showstopper for my work with my machine!
download the drivers here: Realtek