If you are using VHD method of installing windows 8 to virtual disk on physical machine (Scot Hansellman has great tutorial: http://www.hanselman.com/blog/GuideToInstallingAndBootingWindows8DeveloperPreviewOffAVHDVirtualHardDisk.aspx) and you get VHD_BOOT_HOST_VOLUME_NOT_ENOUGH_SPACE error after installation, then your problem is probably dynamic VHD and not enough free space on disk containing that drive. I had the same problem, and googling for it did not solve it, as there is one little catch that is not very known:
You need to have enough free space on physical disk containing VHD that it can contain whole VHD IF IT WOULD GROW TO MAXIMUM DECLARED SIZE! So 100GB VHD on a 90GB free space is a no-go, it does not matter that Windows 8 will use only about 11GB after clean installation.
Windows 8 setup does not check for this, so you may be able to install it, and not able to boot it