The one caveat to this process is that it cannot be done on an active computer, other than that it works incredibly well! First decide whether you are going to use Clonezilla from a USB stick, CD, or ISO for your particular need.
Before creating the image with Clonezilla, you may want to reduce the size of the partition so as to save space of the virtual machine, otherwise you will have to create a virtual disk that is the same capacity or bigger, of the physical machine.
One of the cool new features of VirtualBox 4.1 is the ability to create different types of virtual disks other than the standard vdi, like vmdk (VMware) and vhd (Microsoft). Now you can create these disk types, use Clonezilla to copy the data, and easily convert from one virtual platform to another.
First shut down the machine (either physical or virtual) and boot into Clonezilla. Create your image, or copy the data from device to device if you are converting virtual disk image types, then boot the virtual machine with the Clonezilla ISO as the first device in the boot order. Simply do the previous process in reverse to migrate from virtual to physical.
Don’t forget to adjust your partition sizes after you are done imaging, or create new partitions out of the extra drive space.