You can't make an 800k Mac disk from a PC drive, as (like the 400k disks) they use a different encoding format that PC floppy controllers don't support. (Same goes for every USB floppy drive that I know of; the other problem with USB floppies is that some - most? All? - of them only support FAT12 disk access and not the low-level access needed for other filesystems.) It's probably possible to make a 1.44MB disk from a PC, though.