Dr Mike J Smith
One of the nice things in virtual machines is that you can mount real, or fake, CDs on to the VM. So if you load a CD in to your own system, the VM can access it. Likewise, if you "rip" a CD to an ISO image, you can also mount this. In fact this is the best way to install a Linux OS in to a VM; just download the xubuntu or Fedora ISO image and let things roll.
Virtual Box also has extensions which let you share local folders and so access files on your own system, however it is a bit more fiddly to setup under Linux and doesn't support all distributions. The "quick and dirty" fix is to actually turn whatever files your want to transfer in to an ISO and mount that as a CD.
Now there are plenty of commercial applications that can do this, but that isn't good enough. I wanted a GUI based, open source, solution that can run from a USB stick. And I found it in the form of DoISO which is an open source GUI frontend for the opensource command line mkisofs. And it just works.