Pass these options on the kernel command line: auto=true priority=critical url=http://your.server/foo.seed, and use this preseed file:
d-i debian-installer/locale string en_US.UTF-8 d-i passwd/root-login boolean true d-i passwd/make-user boolean false d-i passwd/root-password password changemeplease d-i passwd/root-password-again password changemeplease d-i partman-auto/method string regular d-i partman-auto/choose_recipe select atomic d-i partman/choose_partition select finish d-i partman/confirm boolean true d-i partman/confirm_nooverwrite boolean true d-i finish-install/reboot_in_progress noteThis will assuredly do thinks you don't want / care about, to make sure to amend it accordingly.