http://www.winbeta.org/guides/how-create-windows-8-bootable-usb


For those who have an ISO of Windows 8 and wish to create a bootable USB rather than buring the ISO to DVD, this guide is for you. Using a Windows 7 bootable USB tool, you can create your bootable USB on a 4GB minimum USB drive.

First, download the Windows 7 bootable USB tool here. After you have downloaded the ISO from Microsoft (or wherever else you may have obtained Windows 8), run the tool, select the ISO, and then select the USB drive. The process is very simple. After it has completed, you will have a bootable Windows 8 USB.