The USB Linux installation enables you to install a portable Linux Operation System on a flash drive . This portable Linux operating system can then be run from any computer that can boot from a flash device, allowing you to bring your operating system, desktop, applications, files, email, personal settings, favorites, games and more with you. It’s your own personal operating system you can carry on in your pocket.

In contrast, if you want to install a Linux distribution from a USB rather than a CD, then click here to follow the guidelines

The install procedure is going trough this tool : Unetbootin

The installer tool is compatible with Windows Ubuntu debian opensuse and gentoo .

To download the tool please go to : http://unetbootin.sourceforge.net/

Under windows start the tool :

Then Click ok to start .

Finnaly you got :

Now restart your computer and from Bios select to start from USB.

Now if you want to install Linux distribution from a USB drive then follow this tutorial

Some more readings

http://www.pendrivelinux.com/
http://www.techradar.com/news/computing/pc/how-to-run-linux-from-a-usb-drive-496211
http://www.unixmen.com/linux-tutorials/206-install-any-linux-on-usb-flash-drive