Tried twice to install archbang to an external drive (ext2/4). Got to the menu choices for root password and for creating default user. Both failed. It seems passwd is not available.
Guessing? The chroot environment has the passwd program missing, wrong place, or wrong permission. Since I'm using a live USB to try this, getting the right code could be a bit awkward, but network does appear to be up. Did not try to get into the chroot environment manually, as things crashed when I tried to stop the error loop that started on user creation.