This is the Video, you are going to see, How Windows 8 Running from an USB Drive. Watch it after the Break.
How to Install Windows 8 on USB Drive/External Hard Drive or Disk
Step 1 – You must have a 20GB or Higher USB Drive or an External Hard Disk of 500GB or more.
Step 2 – If you are using a External Hard Drive, then make a Partition before Installing Windows 8 on That Disk (make a Partition of 50GB and Name it Windows 8 )
Step 3 – Now Insert Windows 8 Developer Preview on the CD/DVD Drive and Connect your USB or External Hard Drive/Disk to the Computer.
Step 4 – Now Restart your Computer
Step 5 – When Rebooting, just Select F2/F8 or Delete to Select the Bios Settings.
Step 6 – In the Bios -> Boot Menu – Ist Priority select CD/DVD Drive and Second USB Drive (If Disabled, Enable it.) and Save it by pressing F10.
Step 7 – Now Installing Windows 8 Starts.
Step 8 – When you come to the Partition Selection Menu, scroll down and the Windows 8 Partition Section and Select that Partition that was in yoiur External Hard Drive/Disk.
Step 9 – Format that Windows 8 Partition and click on Next to Install Windows 8 onto the USB Drive of External Hard Disk Drive.
After 10 Minutes, you can See The Windows 8 Installed on your USB or External Hard Disk. Now once again Reboot your Computer, so that you can See Windows 8 and Otheer Operating System side by Side, and when you Remove the USB Drive or External Hard Drive then you will only see the Other (Windows 7 or Mac OS X) on the Screen.
Watch Video: Windows 8 running on a MacBook Pro from a USB drive via