Virtualbox on ubuntu 11.10

First
You need to edit /etc/apt/sources.list

- gksudo gedit /etc/apt/sources.list

Add the following line

- deb http://download.virtualbox.org/virtualbox/debian oneiric contrib

For ubuntu 11.04 users add the following line

- deb http://download.virtualbox.org/virtualbox/debian natty contrib
Save and exit the file


Download :
- wget -q http://download.virtualbox.org/virtualbox/debian/oracle_vbox.asc -O- | sudo apt-key add -

Update source list
- sudo apt-get update

Install virtualbox 

- sudo apt-get install virtualbox-4.1


Note: Ubuntu/Debian users might want to install the dkms package to ensure that the VirtualBox host kernel modules (vboxdrv, vboxnetflt and vboxnetadp) are properly updated if the linux kernel version changes during the next apt-get upgrade. For Debian it is available in Lenny backports and in the normal repository for Squeeze and later. The dkms package can be installed through the Synaptic Package manager or through the following command:

sudo apt-get install dkms

Source: http://www.ubuntugeek.com/virtualbox-4-1-6-released-and-ubuntu-11-1011-04-installation-instructions-included.html