You cannot convert FFS to SFS without data loss. But as you probably have several partitions, this should not be a big problem.
First create a boot disk (emergency floppy or something like that) and make sure it really works.
Then copy all files from your boot partition to another one. Make sure that really everything is copied (use the Shell or any directory tool like DirOpus). Then install SFS on the HDD using HDtoolbox and change the dostype of your boot partition to SFS. Make sure that your don't touch any other partition but the one to be converted. Reboot with the boot floppy and copy everything back. That's it.
Do the same for every other partition you want to convert.
It might be handy to have a second boot partition instead of the boot floppy because things are faster then.
Bye,
Thomas
