You have to have a machine (virtual or otherwise) already loaded up with Ubuntu, take that image, then deploy that image to another machine (virtual or otherwise). You can’t easily use Fog to push the Ubuntu installer. Also, if you are going to image Linux, you can only have primary partitions of type ext2 or ext3. Fog does not currently support ext4 filesystem, which is the default for Ubuntu. When you install Ubuntu, specify the advanced options during partition and formatting to use only ext2 or ext3 for your non Swap partitions.
In vmware, I think you have to tweak the network adapter settings to make it so the two virtual machines can talk to each other. In VirtualBox, you have to make them both part of the same named network. I do not know the specifics for vmWare.