1 word: FuseISO !
Available via Synaptic or by simply typing:
sudo apt-get install fuseiso
Source: http://www.ubuntu-unleashed.com/2008/04/howto-mount-isos-in-ubuntu-easy-way.html [4]
Links:
[1] http://pulse.veltsos.com/category/it/it-general
[2] http://pulse.veltsos.com/category/it/software/software/os/linux
[3] http://linux.philosweb.com/drupal5/files/Ubuntu_ISOs_2.jpg
[4] http://www.ubuntu-unleashed.com/2008/04/howto-mount-isos-in-ubuntu-easy-way.html