apt-get update && apt-cache search fluxbox
fbdesk - desktop icons for fluxbox window manager
fbpager - a pager application for the Fluxbox window manager
fluxbox - Highly configurable and low resource X11 Window manager
fluxconf - FluxBox configuration utility

apt-get install fluxbox fluxconf fbpager fbdesk

Note that only fluxbox is required. Installing fluxbox *should* create an entry in /usr/share/xsessions for fluxbox. Simply choose it from the Session Type menu in your log in manager (presumably KDM). Save it as default.

If you are booting the compressed image from hdd then simply use a cheatcode.