To be sure you always have the latest version of VirtualBox, you can add the official repository.

Add to /etc/apt/sources.list

sudo pico /etc/apt/sources.list

Add (for your correct version):

deb http://download.virtualbox.org/virtualbox/debian jaunty non-free

deb http://download.virtualbox.org/virtualbox/debian intrepid non-free

deb http://download.virtualbox.org/virtualbox/debian hardy non-free

Add the repository key:

wget http://download.virtualbox.org/virtualbox/debian/sun_vbox.asc && sudo apt-key add sun_vbox.asc

Install VirtualBox:

sudo apt-get install virtualbox-3.0