I have earlier wrote a post on How to install Windows 7 Using a Pendrive or USB drive. But here is a fast way (similar to the method i posted). You may have noticed Installation taking very long time and some times the installation stops by middle all this problems can occur if you use DVD. And whats more the more you Use that DVD drive the bad it will become and we know that. So why not avoid these things and go for a faster and error free installation of Windows. This post is for Experienced Windows Users. All you want is a Windows 7 ISO image and a Pendrive or USB drive with 4 G.B or Greater space. You can install Windows 7 very much faster than installing from a DVD.
Just format the Pendrive to Fat 32 format and copy all the contents of the ISO image using xcopy g: h: /g /h (here g: is the DVD drive and h: is the location of the Pendrive).Now just boot from the thumb drive as usual (To boot from the pendrive set the first boot priority to the Pendrive from BIOS) and you will notice a faster and robust installation of Windows 7.