FYI: "clone of an existing system" is referred to around here as a P2V, short for Physical To Virtual migration. I tell you this so you can recognize the relevance of previous discussions on this site.
Why not just use Disk2VHD
and save all the hassle? VirtualBox supports VHDs, but I personally would next convert the VHD to VDI format using CloneVDI
However, if you insist on doing it the your way then the following linked thread linked discusses several ways to do it. The thread talks about Acronis but the Macrium solution would be the same. Be sure to read the entire thread, as several solutions are given by the end, including the USB option.
Accessing huge Acronis Images After a CD Boothttps://forums.virtualbox.org/viewtopic ... 7&p=109762
NOTE: Regardless of whether you use Macrium or Disk2VHD, it pays to prepare an XP system prior to making a virtual image of it. The necessary preparations are described here
. The wiki is somewhat old, so you should ignore the awful "Step by Step" instructions 3 and 4 for imaging a drive using dd and VBoxManage. Instead image your drive with Disk2VHD or Macrium as discussed above.