I tried this process to install and boot Win8 from a VHD file yesterday and it WORKS!!!

Runs faster than a Virtual Machine and doesn't require you to partition or mess with your existing hard drive nor install a new hard drive to do your testing. You get native speed and support for all your current hardware.

Guide to Installing and Booting Windows 8 Developer Preview off a VHD (Virtual Hard Disk) - Scott Hanselman

Opps...I see our own intrepid Brink has already prepared a tutorial on how to do this.
Windows 8 VHD - Create at Boot to Dual Boot with

Bravo for the GREAT work!