Disk2vhd is a utility that can create live "snapshots" of Windows volumes, allowing you to duplicate/backup systems while running. The program creates Virtual Hard Disk files (.VHD, Microsoft's Virtual Machine disk format) from physical disks and can be used in Microsoft Virtual PC or Microsoft Hyper-V virtual machines (VMs).

The program uses Windows' own Volume Snapshot capability added starting with WinXP to create consistent point-in-time snapshots of the volumes you want to include in a conversion. You can even have Disk2vhd create the VHDs on local volumes, even ones being converted (though performance is better when the VHD is saved to a different disk than ones being converted).