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You can just copy the files inside the directories you mentioned, that is, the virtual harddisk (.vdi) and the xml-based description of the virtual machine. I did this twice, even cross plattform (a XP geust from an OS X host to a Windows XP host, and an Ubuntu guest from a Windows Vista Host to an OS X host) and it worked fine
Ou faça o importar e o exportar seções do manual do usuário. :)