It is really easy. Select the distro you want to boot from, then hit the "Configuration" button which is under the menus of the Virtualbox main window, and once there go to the network tab which is in the left sidebar. Once there you can select "bridge", which will allow having in the guest machine an ip on the same family of ip's than the one of your host machine, else, if you select NAT the guest machine will have an ip looking like "10.0.1.15" or such.
Actually I can't get the network anymore in the live if I don't position it on NAT.