Win7 on virtualbox and full screen mode

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http://askubuntu.com – I've installed win7 on virtualbox on ubuntu 12.04. However, the full screen mode isn't perfect. I have black parts on both sides of the screen. I tried changing the resolution but nothing fits. Anyway to fix this? By the way, my ubuntu is 64-bit (intel 4000 graphic card), and the my win7 is 32-bit. I'm not sure if this is the cause of the issue. (HowTos)