Thank you for these answers, they certainly pointed me in the right direction. But it was a bit more complicated than that.
To work properly, Clonezilla needs a lot of parameters passed to the kernel. I found this, that in the end proved to work: http://clonezilla.org/clonezilla-live/livehd.php
- just in case others want to try the same.
Just remember, when you install clonezilla on a harddisk, you can not make a disk-to-image backup of that harddisk.