Install Ubuntu from a USB stick

"This pages describes how to install Ubuntu by copying the contents of the installation CD to an USB drive such as a memory stick (or flash drive) and making the USB stick bootable. This is handy for machines like ultra portable notebooks that do not have a CD drive but can boot from USB media.

The main steps are:

* Prepare the USB stick
* Boot the computer from your USB stick.
* Install Ubuntu as you would from a normal boot CD

Note: It is highly recommended to use the latest version of Ubuntu to prepare your USB stick."

https://help.ubuntu.com/community/Installation/FromUSBStick