Put a floppy disk (1.44) in your floppy drive (/dev/fd0).
Execute lfr.pl ($ ./lfr.pl).
Answer questions.
Repeat as necessary.
For other ethernet interfaces you need to build a new kernel and possibly
modify the init files in the rootimage filesystem.
$ mount -o loop root.image /mnt
$ cd /mnt
# (make changes)
$ cd /
$ umount /mnt
# run lfr to make new floppy