Why dont just make an image of os3.9 cd and then transfer the image across to your harddrive and then install VirtualCD (can be found on aminet) and just mount the image that way? Then you can just install os3.9 as normal from "cd" on the a1200. Alternatively you could just make a mountlist for a cd drive and not worry about VirtualCD (but the 1st way is easier and less cumbersome and can also be used to easily swap any "cds" you like (has a nice gui).
