I have been doing exactly that from an XP machine for months - opening the HDD on the WDTV as a network share, and copying to it from windows… I now have a win7 machine and although I have mapped it ok and can read files from the HDD on the WDTV, I can no longer copy to the drive from the PC.
I stumbled on a security setting in Win 7 which turns file sharing encryption down to 40 something bit from 128, There is also a setting to allow anonymous access if you want it. Finally I tried copying from the PC using WDTV file management - and that worked. Still unable to initiate the copy from the PC end, but better than nothing.
