Windows 7 and Windows 8 includes support for creating, mounting and booting from VHD images but not many seem to know how to use this functionality to boot VHDs at boot time... I will detail the steps required to have another OS bootable using Windows 7...
This tutorial will show you how to setup Windows 7
or Windows 8
to boot from an existing VHD (Virtual Hard Disk).
All Vista, Windows 7, and Windows 8 (except Windows 8 RT) editions support booting from a VHD.
You must have either Windows 7 Ultimate, Windows 7 Enterprise, Windows 8 Pro, or Windows 8 Enterprise installed on the VHD to be able to boot from the VHD.