you can install gnome once you install knoppix in your hard drive. you can open a terminal as root and type either:

apt-get -t unstable install gnome
or
apt-get -t unstable install gnome-bin

this should do the trick.

if you want kde and gnome on a live cd basis there are several distros that carry them. the one i can think off the top of my head would be pc linux os.

hope this helps!