Add debian-multimedia.org repository to your sources.list file

vi /etc/apt/sources.list

Add this line:

deb http://www.debian-multimedia.org lenny main

Then, update the list of packages

apt-get update

Installing packages necessary

apt-get install debian-multimedia-keyring g++ unzip mencoder flvtool2 python-cheetah python-twisted ffmpeg2theora cortado postfix

Installing Plone and Plumi

Follow the how-to "How To Install Plumi" here