Dang!
Anyway, you problem know this but "Incorrect MS-DOS version" means the fdisk you are trying to run is not the same as is supposed to be run given the version of DOS you are on.
If you boot from floppy and fdisk does not work, your floppy has the wrong version of fdisk. You have to get a boot floppy from a better source.
If you boot from floppy and it works fine and you do whatever and then remove the floppy and boot Windows, you will not be able to use fdisk from your floppy. Windows DOS is not the same as floppy DOS. If your Windows DOS does not have the command fdisk, you are out of luck. Maybe it has been renamed or some other program does that function. In general, I doubt Windows DOS will allow an fdisk type operation. You need to get out of DOS and use Windows utilities.
Mac