Good luck with installing Windows. Just a couple of things. Sound and
networking may not work until you install Windows drivers, just like you
would have to do for a physical installation. This is annoying because
sometimes you need to download drivers and you can't if there is no network.
Catch 22. That is where the shared folder comes in handy. You can download
drivers on the Ubuntu host machine and copy it to the shared folder from
which you can use them in Windows. It is a round bout way of doing it but it
works if you don't have driver disks. Also if you check Passthrough for the
CD drive then you can use it on both Linux and Windows. Otherwise you have
to turn it off and on manually on the bottom taskbar of Virtualbox (icons on
the bottom right of the VM window).