- In VirtualBox, go to Settings -> System, and set CD/DVD as the first in the boot order
- In VirtualBox, go to Settings -> Storage, and under Controller IDE, click on Empty. To the right, click on the small add folder, and select the VBoxGuestAdditions.iso, which is located at C:/Program Files/Oracle/Virtualbox.
- Start the Windows 7 Virtual Machine
- Once booted into the Windows 7 Desktop, at the top, click on Devices -> CD/DVD Devices, and select VBoxGuestAddtions.iso
- At the top, click on Devices -> Insert Guest Additions CD Image. A popup box will appear. Follow the prompts.
Now, after restarting the Windows 7 Virtual Machine, the Guest Additions will have been added. The most notable difference is that the Windows 7 Virtual Machine can now be maximized, and the screen will fill your monitor.