<update date=”March 2, 2012″>
A few comments left below indicating that this workaround works for Windows 8 Consumer Preview as well. I’ve just tried to load W8CP on Virtualbox and confirmed that the Guest additions are still not supported. So this adds additional help to make the Windows 8 Consumer Preview look and work better in your VirtualBox.
Now that you can run Windows 8 Developer Preview on VirtualBox but since it’s not officially supported by VirtualBox yet you don’t have the “Guest additions” that add certain features to the virtual machine, one of which is the screen resolution. You only get to set up with 4:3 ration resolutions like 1024×768. While I believe it shouldn’t be a problem later on, you have a workaround to make Windows 8 work better with your own screen. Thanks to Mister Goodcat for this useful tip.
Let’s say I want to add an additional resolution 1366×768 to fit my widescreen to virtual machine “Windows 8 Preview” I just set up.
1. Run the command from Dos prompt window. Note that the name of the virtual machine is case sensitive.
C:\Program Files\Oracle\VirtualBox>VBoxManage setextradata “Windows 8 Preview” CustomVideoMode1 1366x768x32
2. Then power on the virtual machine. Go to the Screen Resolution, and voola.
And that looks much better.