The Wireless Media Stick will mount 2 USB drives when it is plugged into a PC or media player. The reason for this is that one drive contains the setup wizard files, and the other drive is where your shared files are.
Many media players only show one drive (such as the WDTV series) but many will show two. The correct drive to find your shared files will be labeled Fat32: or WirelessMediaStick : the drive that says Fat16 or WMS Setup is the setup drive.
If you simply have USB1 and USB2 as choices, you might have to go into each drive to see which is which. The one that has the setup files is not the right one, simply open the other drive on your media player and you will see your files.