When you boot an unattended Windows DVD(which contains autounattend.xml), you are directly taken to the installation routine.There is no option to launch the recovery environment.However I found a way of accessing Windows Recovery Environment.
You can create a movie DVD containing a tiny bootable Linux Operating System-GeeXbox.This can play your movies,music on any computer irrespective of whether the computer has an installed operating system or not.
You just have to boot from the DVD media.
The GUI of VirtualBox does not have an option to boot a USB drive (Physical Drive) in a virtual machine.
However you can attach a physical drive to a virtual machine using a command line tool that is bundled with Virtual Box.You can then boot your virtual machine from the attached Physical drive.
Just like how you can boot a computer using a bootable CD,you can also boot a computer using a bootable USB drive.
You can test a bootable USB Drive within Windows without restarting your computer.This is helpful when your motherboard does not support booting from a USB Drive.