You might also try to use the cheatcode fromhd

like

knoppix fromhd=/dev/sda1

On my asus eeepc 900a laptop, I can boot from different filesystems (internal HD, SD card reader, usb drive) using the BBS (bios boot selector) hitting ESC on startup,

however, that only controls the boot code. To actually select which one that knoppix uses, I have to use the fromhd parameter and I can switch between them using fromhd=(sda1, sdb1, or sdc1) (sda1 is internal, sdb1 is SD card, sdc1 is usb drive. if the SD card isn't there, the usb moves to sdb1)