Making an ISO Image of a directory:
mkisofs -o tmp.iso tmp/
tmp.iso is where you want the ISO image to wind up, and where tmp/ is the drectory you want to be the base of the ISO
Making an ISO Image of a CD/DVD:
dd if=/dev/cdrom of=/home/dave/MyCD.iso
Mounting an ISO image:
mount -o loop /home/dave/MyCD.iso /mnt/iso