Windows 7 can be installed from a USB drive when the other installation methods are unavailable. We can choose between a memory card, hard drive which is USB compatible etc., and also several 3rd party tools are available for creating a USB bootable Windows 7 installation media, but I am using the "diskpart" command-line tool. Diskpart is a very good tool as it comes along with your install of Windows Vista, 7 and Server 2008.