Before you actually build your installation ISO, you need to prepare a preseed file to be passed to debian-installer, in order to set some of its parameters and automatically answer its questions.
Open your editor and create a new mypreseed file in your workspace containing the following lines:
d-i apt-setup/uri_type select cdrom
d-i apt-setup/country select enter information manually
d-i apt-setup/another boolean false
d-i apt-setup/security_host string
d-i apt-setup/use_mirror boolean false
d-i clock-setup/utc boolean true
d-i grub-installer/with_other_os boolean true
d-i grub-installer/only_debian boolean true
d-i grub-installer/skip boolean false
d-i pkgsel/install-language-support boolean false
tasksel tasksel/first multiselect standard
This example preseed file instructs the debian installer to use the CDROM drive as main APT source media and to automatically install the standard task, which will pull all packages of your Ubuntu/hardy remix.
You can now actually build your installation media.