In this video Jeremy Chapman senior product manager from the Microsoft enterprise product management team talks about booting from VHD as well as some of the new imaging features.
By the way, note that when booting Windows 7 from a VHD file you cannot use Windows Bitlocker or the Advanced Power Management features. Hibernation mode is also not supported.
The Boot from VHD in Win7 video is published here.
Additional information around native VHD support in Windows 7 can be found in this blog post.
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