The RedHat boot disk boot.img is in MS-DOS format, using the
SYSLINUX program to boot up. The supplementary disk
supp.img is a Linux ext2 filesystem. If you have
support for the loopback filesystem in your Linux kernel, you can mount
both of these files in your filesystem and hack at them:
# mkdir -p /mnt/boot /mnt/supp
# mount -o loop -t msdos boot.img /mnt/boot
# mount -o loop supp.img /mnt/supp
Now you should be able to see and manipulate the files on the boot and
supplementary disk under /mnt/boot and /mnt/supp
respectively. Phew! Note that older versions of mount may
not be able to handle the -o loop option. In these cases
you'll need to explicitly use losetup to configure the
loopback device for each file, e.g.
# losetup /dev/loop0 boot.img
# mount -t msdos /dev/loop0 /mnt/boot
You might also need to explicitly use the -t ext2 option when
mounting an ext2 filesystem like the one on the supplementary disk.
But, it looks like people with modern Linux distributions shouldn't have to
worry about this.
Of course, if you don't want to mess around too much, you can cut a corner and manipulate actual floppy disks rather than these floppy disk images. If time is important, you'll probably prefer to use the loopback devices, since you can hack around with the disk images without incurring the latency associated with a genuine floppy disk read/write.