I'm not on my own rig now so can not make specific actual screenshots, but first thing for you to do is to open settings for your Windows virtual machine, select Display
from the left pane and set video memory to max (128 MB) and enable 3D Video Acceleration
(see screenshot on this
tutorial, part 1
; tutorial is for Linux but procedure and settings are the same).
Secondly, if not already installed you need to install VirtualBox Guest Additions
for better integration between host and guest (screenshot here
, part 2
; it's a tutorial on installing Linux on VirtualBox but the menu from where you'll find Guest Addition link is the same).