At this time, Apr 2012, the Basic File Sharing on the Wireless Media Stick will only share from the C: drive of the windows PC. If you have other drives, or other partitions other than C: you will need to share a folder on the C: drive, and then create symbolic links to the other folders on the other drives. Please see here for instructions:
Creating Symbolic Links in Windows
In a nutshell, you would share a directory on C: such as C:\shared (just for an example). Then if you have a directory called D:\Movies (or any other directory) that you want the stick to see, you would create a symbolic link in the C:\Shared directory pointing to D:\Movies. Think of it like a shortcut.
You would run a command like this:
c:\mklink /D C:\Shared D:\Movies
This will create the directory (/D) link from the C:\shared folder to the D:\movies folder, which basically creates a folder c:\Shared\Movies. Remember, the Movies directory is on the D: drive. When you run the Add/Remove folders on the stick, simply pick the C:\Shared folder, and it will be able to stream your d:\Movies folder.
You can do this procedure with multiple drives and folders (such as USB drives, etc).