From live cd:
#init 3
#su knoppix
$ su
# startx $(which fluxbox) -- :1

A new Xsession using FLuxbox is started on screen 1.
Use Alt +F4/F5 (from cd) and Alt + F6/F7 (hdd install)
to toggle back and forth from screen 0 and 1

You can simply toggle to another VT w/ CTRL+ALT+F2 (for example) and do the same but do it as USER! not root.