As part of my C programming course recently I needed a Linux environment to work in, so decided to give Sun VirtualBox a try as a way to run Ubuntu 9.10 on my Laptop (running Windows 7).  It works well, but required a little tweaking to get going properly.

First, you need to install guest additions - to do this you need to choose it from the devices menu at the top of the VirtualBox window... this mounts them as a virtual CD ROM drive in your Linux install.