Great! 

I just installed Windows 8 CTP in Hyper-V as a virtual machine.  I then set it up to boot to VHD.  All went well!

How to do this (After installing Win 8 CTP as a VM):

1. From Server Manager (remember, this is on the Windows Server 2008 R2 parent platform running Hyper-V), expand Storage.

2. Right-click Disk Management, select Attach Virtual Hard Disk dialog box, click Browse.

3. Browse to the location of the .vhd file for Windows 8, which in my case was d:\Program Files\Microsoft Learning\Windows8, and select the .vhd file, in my case I had named it windows8.vhd. Click windows8.vhd, open, then OK. note the drive letter that Windows associates with the attached .vhd. In my case, it was F:\.

4.Click Start, go to Command Prompt, right-click it and select Run as Administrator. Yes, if required, to the UAC pop-up.

5. At the command prompt, type bcdboot F:\windows Note I used the drive letter Windows assigned in 3 above.

6. At the command prompt, type bcdedit /set {default} Description Windows 8

7. At the command prompt, type shutdown /r /t 0 The system reboots.

8.  Select Windows 8 as in the boot menu.  Enjoy!