The first,

You open the "terminal" way (alt + f2) and type "xterm"

second,

after the open, add a key to download virtualbox

root @ bt: ~ # wget-q http://download.virtualbox.org/virtualbox/debian/oracle_vbox.asc-O-| sudo apt-key add -

third,

install virtualbox update by first key is added

root @ bt: ~ # sudo apt-get update

root @ bt: ~ # sudo apt-get install virtualbox-4.1

because in my notebook is already available, the display case of the above.