Mounting ISO9660 read-write?

["Gary Hennigan" <glhenni@sandia.gov>]

I've got an image of a CDROM that I created with 

	dd if=/dev/cdrom of=image.iso

It's an installation CD for some software and the installation script
is bombing so I thought I'd copy it to an ISO image, mount it
read-write, and tweak the install scripts to find the problem. Trouble
is no matter how I mount the darn thing it's always read-only. I do:

        mount -o loop,rw /usr/tmp/image.iso /mnt

and it mounts fine but,

        % cd /mnt/Unix
        % touch junk
        touch creating `junk': Read-only file system

sure enough

        % cat /proc/mounts
        /dev/loop0 /mnt iso9660 ro 0 0


I've tried a couple of iterations of mount with no success. Any ideas?
Is there some property of the CD image that keeps me from mounting it
read-write? I know I've created ISO images by hand and mounted them
with loop before burning a CD and never had this problem, but I can't
recall every copying a CD image, mounting it and modifying the
contents.

Thanks,
Gary