Well one thing can be done. Run Virtualbox, and add a new hard disk larger than the first. Then format the entire "hard disk" to ext4, mount it, and back up the entire image of first hard disk/partitions into the second hard disk in Virtualbox. (using dd)
Access the share in your host, and you should get the image.
However I doubt transferring your Virtualbox's installation will be that simple.
Well, the way I understood the problem is, that the OP needs to copy files FROM the .vdi file (which is the virtual hard disk, on which Linux is installed), to a Real physical hard drive.
Now assuming that a Pen Drive works in the Virtual Linux that is installed, can't OP just copy the entire files present on the disk and copy it to the Pen drive.
Then paste the entire contents of the pen drive to the physical drive, from the host OS.
Havn't worked on Linux, so don't know if this could work. But I would have followed this procedure, if I had to clone the contents of a Virtual Windows.
Nope. Will copying contents of C: from one PC to another transfer a Windows installation?