I managed to do this in the end, here is an overview of what I did.
- Create a vhd and mount it (see guide)
- Copy the contents of Windows.old to the mounted vhd
- Installed Virtual Box (Microsoft Virtual PC cannot cope with 64 bit virtual clients)
- Unmounted the vhd from windows and used it to create a new Virtual Box instance
- Kicked off the new instance and booted to a windows 7 install cd
- Using the Windows 7 boot cd recovery options I opened a new command prompt
- Using Diskpart.exe I set my primary partition to be Active (see guide)
- Used Bootrec.exe to create a new MBR and rebuild the Boot Configuration Data (BCD) store (see guide)
I was then able to boot into my vhd. My old windows 7 install then went through a number of automated driver updates due to the new virtual hardware configuration. After a few reboots it was fine though. Note, I did need to reactivate windows though due to the hardware changes.
Hope this helps anyone else trying to do the same.
bootcfgon your virtual disk, if that identifies your windos installation as a valid OS, you can then fix the other things.... – Mallik Mar 5 '12 at 13:32