Microsoft published a guide about creating a portable Windows 8 environment with Windows To Go

Windows To Go is a new feature in Windows 8 Enterprise Edition that enables you to provision a USB drive with a complete, managed Windows 8 system image. You can insert the USB drive (known as a Windows To Go workspace) into any Windows 7 or Windows 8 host computer to boot and run a managed Windows 8 system without installing any software on the host computer. This guide shows you how to create a Windows To Go workspace.

  Creating a Portable Windows 8 Environment with Windows To Go