> sudo apt-get install apt-get is a tie-in command for Ubuntu's own package manager with its own software (that is downloaded and installed through tools like Synaptic, Add/Remove software, or apt-get). Installing any other file ever you downloaded, even when they are .deb files (the file type that the package managers actually download and install), will not work. Just making this clear as proper instructions have already been given by John Drescher and dimesio.
