This is specially useful for netbooks and ultrabooks that do not have a DVD drive.
0- Backup your data before installing Win7.
1- Make sure you have a .ISO file with the Windows 7 installer.
2- Download and install the “Windows 7 USB/DVD download tool”.
3- Insert your USB drive in the computer you are using to prepare.
4- Launch the “Windows 7 USB/DVD download tool” and follow the steps.
5- The USB drive is now ready, plug it in the netbook/laptop/ultrabook where you want to install Win7 and turn it on.