It might be that your usb devices are listed under something other than sda. Does it list your usb devices when you type
or
? I've never used DSL before, so I don't know the specifics of it, but it sounds like you just need to figure out what name it's assigning your device to. (assuming it sees the drive in the first place)
This is just a hunch, but you might also have to have the drive unmounted in windows before linux will be able to take control of it.