Adjust your repository settings :

Add one of the following lines according to your distribution to your /etc/apt/sources.list:

vi /etc/apt/sources.list ( package in this case is virtualbox ).

deb http://download.virtualbox.org/virtualbox/debian maverick contrib
deb http://download.virtualbox.org/virtualbox/debian lucid contrib
deb http://download.virtualbox.org/virtualbox/debian karmic contrib

save file then run the kernal update :

apt-get update

then run :


sudo apt-get install virtualbox-4.0 (this will fetch and install the software).