OK,
First of all I want do this, having the original firmware in my sansa. When I say hide, I mean, that I want to have the mp3 files active to play in the sansa, but if you connect the device to the PC, and navegate the folders with the explorer, you can't cut, copy, delete and modify and neather you can't see them. The files would be ghost. There are some demo music when you buy the sansa, that you haven't got access by the explorer, I want to put mp3s in the sansa and do the same.