just a copy-paste list:
sudo sh -c ‘echo “deb http://download.virtualbox.org/virtualbox/debian karmic non-free” >> /etc/apt/sources.list.d/virtualbox.list’
wget q http://download.virtualbox.org/virtualbox/debian/sun_vbox.asc -O | sudo apt-key add – sudo apt-get update
sudo apt-get install virtualbox-3.1