To install it in Ubuntu Jaunty, open a terminal and:

1. Add the repo:

sudo sh -c "echo 'deb http://ppa.launchpad.net/inkscape.testers/ppa/ubuntu jaunty main' >> /etc/apt/sources.list"

sudo sh -c "echo 'deb-src http://ppa.launchpad.net/inkscape.testers/ppa/ubuntu jaunty main' >> /etc/apt/sources.list"

2. Import the Launchpad key:

sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys B9DC2CA0

3. Installation:

sudo apt-get update && sudo apt-get dist-upgrade

Screenshots:

Update:

If you are still getting errors about the PPA key, use this script the final version of Inkscape 0.47 is out. Read HERE how to install it.