On your win7 pc, open media player, make sure all the media you want to share has been detected otherwise import their location in the media player library manager, While in the libraries view click the stream menu and enable Automatically allow devices to play my media
Next, click the Stream drop-down menu again, and select More streaming options. On the resulting screen you can name the media library. The screen will also show a list of devices on the network that are capable of accessing the library. Make sure your WD's are allowed
Your WD tv should now be able to find and play the files.