Converting a virtual drive from Virtual PC (.vhd) to VirtualBox (.vdi)

I wanted to make a copy of a Windows 7 virtual drive.  It was created with Virtual PC (.vhd) and had been running under VirtualBox as-is.  Can't make a simple copy because the Virtual Media Manager will complain about duplicate UUIDs.  So might as well convert it into VirtualBox's .vdi format--the process will also generate a new UUID.  Use the CloneVDI tool.