I need to change my client OS from Windows 2008 to Windows 7. I therefore need to convert all of my HyperV images to Virtual Box.
What is the best way to do this? Or is there a way to run HyperV on Windows 7?
Virtualbox does actually support importing VHD file, unfortunately this is only for VHD's created with Virtual PC, not Hyper-V, which adds some additional information to the VHD. Some people have successfully got VHD Vm's to boot by ensuring the VM in Virtualbox uses an IDE rather than SATA controller.
I'm not aware of anyway to convert VHD's straight into virtual box, however you can convert VHD files into VMWare VMDK files (using tools like Starwind V2V) which Virtualbox is then able to use.
This did the trick for me:
VBoxManage clonehd input.vhdx output.vdi --format VDI
I added this new disk as an IDE drive ("PIIX4") as suggested here and enabled System/EFI Setting for this VM.