Copy the liveusb image to your usb key

"First of all make sure you have completely downloaded the image and checked the shasum. Once that is done you have to copy the image to your usb device. Note that you have to copy it to the device and not a single partition. NOTE: THESE COMMANDS WILL DESTORY ALL CONTENTS OF YOUR USB KEY, REMEMBER TO BACK IT UP!"

http://blag.chaox.net/support/copy-the-liveusb-image-to-your...