These are required for features such as shared folders, shared clipboard and (in windows) video-drivers. They are installed on the guest.
(tested on 12.04 amd64)
The version of theguest-additions in the official repos (4.1.x)
doesn’t work - you need > 4.2.
If you’ve installed virtualbox on the host
using oracles repo (or downloaded binaries)
you can install the guest-additions on the guest
by following these instructions:
sudo apt-get install dkms build-essential linux-headers-generic
(?)sudo mount /dev/cdrom /media/cdrom
cd /media/cdrom && sudo sh VboxAdditions
Do essentially the same thing as on ubuntu, but cdrom is of course mounted automatically.