>> The drive letter problem is something that would have to be fixed via the OS. <<
We had smaller, plain USB drives before and they never exhibited these problems. The problem with the Buffalo units is that (1) they mount as CD's and not USB drives (they are detected as CD's in Device Manager) and because of this, they (2) cause the drive letter assignments to change when there is more than one Buffalo unit plugged in. All CD's mount with the lower drive letters, assigning the USB secondary partitions of the Buffalo units a higher drive letter. If I plug a second Buffalo unit in, the backup partition that had been G: becomes H: If I unplug the Buffalo, the drive letter does not return to G: This causes the backups to fail.
I don't know if there is a way to "fix" this with the OS. And, if I read the posts in this forum correctly, there is no way to remove the CD partitions of the Buffalo drives. Looks like we'll have to find another solution and use the Buffalo units for something else.