One option to mount and unmount ISO files in Ubuntu is to use the fuseiso package. First install the package using the name fuseiso.
To mount a ISO file, first create a directory where it can be mounted and then mount it:
$ mkdir dir-to-mount-iso $ fuseiso foo-disc.iso dir-to-mount-iso
To unmount the ISO file, unmount the directory where it was mounted:
$ fusermount -u dir-to-mount-iso
Tried with: fuseiso 20070708 and Ubuntu 12.04 LTS