[ Thanks to Ken
Leyba for this link. ]
“Now the folder needs to be accessible to the guest
Ubuntu. In the running instance of Ubuntu, from the Virtual Box
menu select Devices -> Shared Folders… In the resulting Shared
Folders dialog box, select Machine Folders, then click on the
folder icon with the plus sign in the upper right. In the Folder
Path: drop down box select Other… and navigate to the folder
created in the Vista host. The Folder Name: text box will be filled
automatically, it can be left as the default. Add a check to the
Make Permanent check box, the shared folder will be always
available to the Ubuntu guest. Click OK in the Add Share and then
Shared Folders dialog boxes to complete this step.”