To add these repositories, run the following commands in a terminal (command available for Ubuntu Karmic only, because there aren't any packages available for older Ubuntu versions; Lucid packages will probably be available soon):
sudo add-apt-repository ppa:gloobus-dev/gloobus-preview
sudo add-apt-repository ppa:gloobus-dev/covergloobus
And then to install both Gloobus Preview and CoverGloobus:
sudo apt-get update && sudo apt-get install covergloobus gloobus-preview