XP Mode uses a main read-only VHD and then a "differential" VHD to account for the changes you make in XP. The only way I know of that you may want to seriously get back into using your older Virtual PC VHD is to convert it for use for VirtualBox or VMWare Workstation. XP Mode is specifically designed as a sort of compatibility virtualization, and not an entire virtualization suite (even though it apparently uses an integrated and unobtainable version of Virtual PC 2010(?) ). I would recommend an attempt as using third party virtualization software under this scenario.