This video from “midfingr” is a very nice demo of installing Ubuntu Linux on Sun’s Virtual Box. If you are running vista and want to run Linux, this a good option.
If you do not find the VBOXADDITIONS. Restart Ubuntu after the part 1 of the install. Devices > Install Guest Additions…. You should be able to mount the VBoxGuestAdditions.iso.
Here are the install steps for Ubuntu 9.04 :
Install Ubuntu 9.04
Enjoy the freedom of Open source !