Windows 7 USB/DVD Tool
The Microsoft 7 USB/DVD tool is a freeware program that allows users and administrators to create bootable media from operating system ISO image files. This makes installing an operating system from an ISO image file a very easy process without the necessity of having a DVD or DVDROM device. All you need is a USB Flash and the ISO image of the operating system you want to install.
Detailed instructions can be found in our How to Install Windows Server 2012 from USB Flash – ISO Image article.