I was wanting to try the new Theme manager for KDE 3.3 so I installed it on Knoppix 3.4 HD install. Here is a brief explanation of how I did it:

1. Leave deb sources in /etc/apt/sources.list as the default and add:

deb ftp://ftp.debian.org/debian testing main contrib non-free
deb ftp://ftp.debian.org/debian unstable main contrib non-free

2. restart in text mode, linux 2
3. login as root and apt-get update
4. apt-get install kde -t unstable
5. You will get an error of broken pipe with kontact-plugins type
dpkg --force-overwrite -i /var/cache/apt/archives/kontact-plugins_4%3a3.2.3-2_i386.deb
(type this all on one line and modify the version of kontact-plugins to match yours)
6. type apt-get install kde -t unstable again
7. apt-get install kdebase -t unstable
8. apt-get --reinstall kdm -t unstable
Note: at each of the prompts to keep or overwrite my config files I chose the default (n)
I hope this helps.
Larry