Some PC HD drives have jumpers on them (like Sony) that allow you to use one as a DD drive in the A4000. You still need to type in the diskchange command in a shell window to get the drive to look for the disk but it works.
You won't be able to get a PC HD drive to operate as an Amiga HD drive without extra hardware, because the Amiga HD drives slow down to something like 150 rpm to write double the number of tracks on a disk to deliver high density. PC drives do this differently for high density; though regular double density should work okay.
