By default, it looks like the device mounts as MTP when you connect via USB (media transfer protocol).
[See:
http://en.wikipedia.org/wiki/Media_Transfer_Protocol]
There is a tutorial on the Memorex Electronics website:
[See
http://memorexelectronics.com/html/downloads.php]
Look for "MMP8565 Digital audio player with 1GB flash memory"
And the "Product Tutorials" for a pop-up tutorial.
(Note: The MMP8568-HIT looks pretty close to MMP8565).
However, I found that if you hold down the Play/Pause button while connected via USB, it will change to mounting as USB Mass Storage Device Class (USB MSC).
[See:
http://en.wikipedia.org/wiki/USB_mass_storage_device_class]
This will make the media player look like another USB flash drive, and let you see it as a removable disk drive (e.g., "F:")
From there, I see:
F:\MUSIC
F:\PICTURES
F:\PLAYLIST
F:\VIDEO
And, Windows Media Player also sees the files.
Simply drag-n-drop to the directory (e.g., using Explorer) to add/remove files from the MP3 player.
I prefer this method, as I don't need to use Windows Media Player at all.