I don't know how to install the nvidia driver on a Knoppix hdd install. I do know however that Kanotix makes a great Debian SID installation and to install the nvidia driver (whichever version you want) you simply do this:
Code:
CATL+ALT+F1
install-kernel-source-vanilla.sh
install-nvidia-6629-debian.sh
That's it! The scripts will download and patch the kernel source for your kernel, download the nvidia driver, build it and restart X for you.