The unofficial Windows 8 Beta Blog published a tutorial about making Windows 8 Consumer Preview portable

You will need:

USB Stick or External Hard drive
Must be greater than 16GB
Preferably USB 3.0
Lots of Time
I have also created a video where you as how to port Windows 8 consumer preview on external drive. You can view the video or continue reading the article

  Make Windows 8 Consumer Preview Portable