I installed Windows 8 RC in VirtualBox with 25G virtual disk size, which squeezed with Office 2013 and Visual Studio 2012. Then, only 2G disk space is available. Now, I have two options, 1. Reinstall the Win8 2. Inscrease VHD size.
Thanks for this blog entry, I found the solution.
Then, go to Win8 disk management to extend the disk size.