VirtualBox 2.1.0 for Ubuntu 8.10

Debian-based Linux distributions: Add one of the following lines according to your distribution to your /etc/apt/sources.list:

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

Download and register:

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

The key fingerprint is

AF45 1228 01DA D613 29EF  9570 DCF9 F87B 6DFB CBAE
Sun Microsystems, Inc. (xVM VirtualBox archive signing key) 

To install VirtualBox, do

apt-get install virtualbox-2.1

Replace virtualbox-2.1 by virtualbox to install VirtualBox 1.6.6, or replace it by virtualbox-2.0 to install VirtualBox 2.0.6.

Note: Ubuntu users might want to install the dkms package (not available on Debian) to ensure that the VirtualBox host kernel modules (vboxdrv and vboxnetflt) are properly updated if the linux kernel version changes during the next apt-get upgrade.

Source: http://www.virtualbox.org/wiki/Linux_Downloads