You will also want to follow these directions on the
www.VirtualBox.org site
Note: Ubuntu users might want to install the dkms package (not available on Debian) to ensure that the VirtualBox host kernel modules (vboxdrv and vboxnetflt) are properly updated if the linux kernel version changes during the next apt-get upgrade.
Also, you will need to install the GuestAdditions.ISO, along with reading
the information here:
http://www.virtualbox.org/wiki/User_FAQ
on Windows Shared Folders with a Windows GUEST VDI.
And don't forget the HOWTO's and TUTORIALS.
lkraemer