The following command converts a hard-drive image file in VMWare format (vmdk) to a Virtual Box hard-drive image file (vdi):

"C:\Program Files\Oracle\VirtualBox\VBoxManage.exe" clonehd --format VDI "harddrive.vmdk" "harddrive.vdi"

modifyhd can be used as parameter to VBoxManage.exe in order to resize a hard-drive. This example will expand a Virtual Box hard-drive image file (vdi) to 40GB. The size after –resize is given in megabytes:

"C:\Program Files\Oracle\VirtualBox\VBoxManage.exe" modifyhd "harddrive.vdi" --resize 40960