sandisk - usb mode

I have a Sandisk e250 mp3 player, configured to act as a usb drive when 
connected to my PC.  I have been loading directories of mp3s to it, and it 
organizes them into a database and plays them in several ways.  It works 
well.

When I try to erase the directories, I've been left with a few "garbage" 
directories, i.e., those with valid names but garbage files within them, and 
I can't get rid of them.  Some of the entries are pretty large sized, so that 
I've lost a couple of hundred megabytes, and I increase the size of the 
garbage section, and lose more room, everytime I wipe the disk.

I don't know what kind of file system it uses.  Is there a disk editor I can 
use to get rid of this mess and get back all the room I've lost?
-- 
The Roman Rule
	The one who says it cannot be done should never interrupt the
	one who is doing it.