Scenario:

Snow Leopard (Mac OSX) as host, Ubuntu 9.10 as guest (Virtual Box virtualization).

I want to share files from Leopard to Ubuntu.

1. Create a shared folder in VirtualBox — Ubuntu guest settings



2. Create mount directory in ubuntu

   sudo mkdir /mnt/Downloads

3. Mount share (created in step one)

   sudo mount.vboxsf Downloads /mnt/Downloads/

URL: http://blogs.sun.com/tao/entry/virtual_box_shared_folder_between