If you want to Drag and Drop files using explorer make sure that the device is in the MSC mode.
This way the device is in the Mass Storage Class and it should show up in my computer as a device with removable storage.
Then just copy music to the Music folder.
This Video Shows exacly how to copy music in MTP mode.
http://mp3support.sandisk.com/mp3/draganddropmsc.wmv
