Download Fabianx's install script
Open a shell and make it executable like this
Code:
chmod +x nvidia-live.sh
Run it:
Code:
./nvidia-live.sh
The Nvidia drivers should the be automatically downloaded, you will be asked a few questions and then the drivers will be installed.

I've used this several times and it works great.

One caveat: if you are trying to run this script on a hard drive install of Knoppix, you will receive an error at first, but then the script will download the proper hard drive install version. After it does that, simply repeat the steps listed above on that new script.