http://drupal.org/project/quickstart
Under ‘Installation:’ after point 4, add a bullet…

Install VBox Guest Additions.
With the new machine running, select Devices>Install Guest Additions …. (autoruns)
Reboot VBox and the new machine
VBox ‘Guest Additions’ will make your life much easier by providing closer integration between host and guest (mouse pointer, shared folders, seamless windows etc.). In the future if VBox software is upgraded It is important to also upgrade Guest Additions by repeating the process above.