MacBook Air phantom files I deleted all of my files and even did command/power-command and reinstalled OS X Lion. But I still don't have all of my hard drive space available. When looking in About this Mac it shows 12GB of audio, movies and photos of which there are none.

Where are these files and how can I delete them to regain my HD space? I'm trying to bring my MacBook Air back to new and start clean.
Download and run a free tool like Disk Inventory X or OmniDiskSweeper. It will point out where disk space is being used, by which files/folders and also allow you to delete them from the tool.

There are also paid applications that have similar features, like DaisyDisk.