Here's a quick tutorial from the wiki that's being tested ATM:
To transfer an ADF file to an Amiga-formatted floppy disk is a multi-stage process. To begin with, you must realise that the PC floppy controller simply can't write or read Amiga disks (Disk2FDI, a cunning hack, can only read). So the ADF file needs to be transferred to the Amiga.
The easiest way is with cables. The most straightforward one is a NullModem? cable, connect it between both computers, then using a decent terminal program on each end, z-modem it over (a process that should take around 3 minutes per uncompressed .adf). There are more complex ways going over TCP/IP, either you already have that set up or z-modem will be easier.
Alternatively, you can use more disks. AmigaOS2.x and above can read MS-DOS formatted double density disks, and there is a program called "CrossDOS?" for other versions. So format a disk as double density (720k) on the PC. It doesn't matter if you only have high density disks - simply put a piece of tape over the hole opposite the write-protect hole.
Now you've got a disk that both systems can read, but the ADF won't fit on it. One way to solve this is to compress it using a tool that both the Amiga and the PC can understand, such as LHA or Zip. If that doesn't work for you, you can split the file, which while trivial in computational terms is fairly complicated to actually do given different OSes and software. Once you get it in bits on the Amiga tho join command should be able to put it back together.
Once you have reconstituted the ADF on the Amiga, then you simply need to insert a blank disk and use a tool such as ADF2Disk from Aminet to write the ADF file.
