Earlier this week I wanted to install the new Windows 8 Consumer Preview on my machine. I already had the Windows 8 Developer Preview installed on a VHD - I believe I get a better performance out of the system than using virtualization software. So at first I tried to launch the installation from within Windows 8 Developer Preview, but I failed.
I then went to Scott Hanselman's blog post on installing Windows 8 on VHD, but he also ducked the topic by simply writing "Updating from Developer Preview? Delete and start over!". The steps he then describes to install the new version (delete the VHD, remove the boot entry, setup a new VHD, configure the system to boot from the VHD, install) are very useful and easy to follow, however I would like to provide an alternative approach which I found to be even easier. This method does not provide an approach to upgrade the system, but it does not require any configuration regarding the system boot at all, given that your system already boots from a Windows 8VHD.
The usual disclaimers apply: it worked on my machine, but it might not work on yours. Be sure that you know what you are doing, and don't call me if it does not work. There is no support, and you do everything on your own risk.
Here is what I did:
Go to disk management and attach the VHD so that it gets a drive letter (in my case, W:)
In Windows Explorer, right-click on W: (or whatever drive letter the VHD is using) and choose Format. Use the quick format option; this deletes everything on the VHD. Make sure you know what you are doing, and make sure you chose the right drive letter! If in doubt, make a backup of the VHD.
Back in disk management, detach the VHD so that it does not have a drive letter any longer. Do not choose to delete the VHD - just detach it.
Follow Mister Goodcat's instructions to install Windows 8 to the VHD, just follow the step "Create the Windows Image"). In short: download and extract the Windows 8 ISO, download the Install-WindowsImage PowerShell script from MSDN, and run it from a PowerShell command window. The command line I was using is shown in the image below; check if all options (location of install.wim, targt drive letter, and so on) match your system.
Since your VHD is already known to your boot manager, and is also bootable (thanks to Windows 8 Developer Preview being on the VHD previously), you can stop here. No need to run bcdboot, no need to edit your boot configuration.