make a image with eg. 
ddrescue
 or Clonezilla
 or SystemRescueCd
 or Disk2vhd

dd if=/dev/sda of=/wtf/ImageFile.dd

Convert image into a virtual disc

VBoxManage convertfromraw ImageFile.dd OutputFile.vdi

Create a new VM and boot it :-D

Windows needs special care: Migrate_Windows