like you already know, its depend on the order of which device is connected first.
As your Back-up software, probably you made it automatic .. I prefered manual, so it will ask the source and destination disk.
Does anyone know how to make sure that a given USB drive (external HD, jump drive, camera that acts like a disk drive, etc) always gets the same drive letter. Ideally I'd like to reserve J for the external HD, K for the MP3 player, etc. I'm running windows XP Pro with the latest patches.
The only way I know of doing this is to follow a strict plug-in / power-up procedure when starting the PC or to (manually) fiddle with the drive assignments.
Unfortunatly my automatic backup software isn't very smart and once tried to back up my (internal) hard drive to my mp3 player.. because the mp3 player happened to grab the drive letter normally assigned to my external HD. Naturally this didn't work.