Hi Samuel,
thanks for your reply. I guess that my CD/DVD reader supports several modes, since if it really wouldn't be supported by Debian Hurd, then the installation process couldn't even reach that stage, isn't it? That's what makes me feel confused about it.
By the way, later this day I tried to install it in a VM (Virtual Box under Windows), where this problem didn't occur, but it just crashed somewhere in the middle of the installation process, while it was installing some packet (I could reproduce this and take a screenshot if anyone should be interested). Basically Debian Hurd SHOULD definitely be able to work in a Virtual Box VM, isn't it?