Windows 8 CP USB

Putting Windows 8 Consumer Preview on an external drive in a USB enclosure or on a USB flash drive is possible.

Here's what you need.
A PC running Windows 7 or Windows 8 beta;
The Windows 8 Consumer Preview ISO formats
The Download: Windows® AIK for Windows® 7 - Microsoft Download Center - Download Details
A USB storage device (at least 30GB)

Here's how I did it.
First, the USB drive needs to be prepared for the image by using Windows' diskpart command-line disk partitioning utility to re-partition and format it as a bootable NTFS drive. From an administrator-level command prompt:
•Run diskpart
•At the DISKPART> command prompt, enter LIST to find the USB device's disk number.
•Select the USB as active by entering SELECT DISK and its disk number (for example, if the USB drive is listed as disk 2, enter SELECT DISK 2 )
• Purge all the existing partitions from the USB by entering CLEAN
•Create a new partition : CREATE PARTITION PRIMARY
• Quick-format the partition as bootable NTFS: format fs=ntfs quick
•Set the partition as active: ACTIVE
•Leave diskpart by typing in EXIT

The next step is to create a new folder,name it and put the install.wim from the W8CP sources folder and the imagex.exe from the AIK Tools folder.

I'm using 64bit so I opened the Tools amd64 folder and copied all the files into the folder with install.wim

I named my folder W8CPUSB and my USB drive is D:

Now from an elevated command prompt:

type cd ..
cd \W8CPUSB
W8CPUSB>imagex.exe /apply install.wim 1 d:/

When that completes the USB drive needs to be made bootable.

At the same elevated command prompt

W8CPUSP>bcdboot.exe d:\windows /s d: /l ALL

Now you're ready to boot from the USB drive.

First you will see the W8CP Beta Fish>

Updating Registry
Preparing
Installing Devices

When this all completes you should be into Windows 8 Consumer Preview where it asks for the serial key.

The rest is the same as a regular installation.

I got most of the idea from this link but I needed to change the command line entries to get it to work.
Ordering "Windows to Go": how to create a bootable Windows 8 USB thumb drive

I have it working on a 32GB flash drive and a SSD in an external box.