I have a test Fog Server currently running off of Virtual Box. When you are using Virtual Box you need to make sure the settings for network adapters (on Virtual Box) are set to bridged and that is using the ethernet port of your Host box. Below is an example of my settings. The installation of Fog itself is the same as the user guide. If you are connecting your client computer to your host computer and are using Windows you will need a cross over cable or a switch to get this to work as well. Hope that helps.
[url="/_imported_xf_attachments/0/103_Network Settings for VBox.jpg?:"]Network Settings for VBox.jpg[/url]