USB Windows 7 Installer : Install Windows 7 via USB Flashdisk
Good news for you who have laptops and want to try the power windows 7 but your laptop does not have a DVD drive so do not worry, Microsoft has officially released a tool, called Windows 7 USB / DVD Download Tool (WUDT) so you can install windows 7 without going through external DVD. This single innovation would make it easy for the netbook or notebook users who do not have the internal DVD player. This tool also allows you to have a bootable installer using the downloaded install files on a USB flash drive.
Source : www.everythingusb.com