This is what you will need
Computer that can boot with USB thumb drive
USB with 4GB of space, new version only requires a 1 GB drive.
A version of pre build Chromium OS - I will show you where to find it.
Preparation - This instruction will show you how to use a pre build version of the Chromium OS, thus you won't need a linux machine to build it from source. You can start by downloading a pre-build version of the Chromium OS. There is a version online made by Hexxus which is good to go and easy to install on any USB drive. Use the Windows Version or Mac instructions to write that image to your USB drive.
Caution - Major issue with Chromium OS is that the hardware drivers are still in development stage. Therefore it might be hard to get a few hardware to function, most errors reported were sound device or wifi drivers. If there are any keyboard or Mouse problems, try to connect a USB version of it.
Boot up - Chromium requires your computer to be able to boot from USB, and once in the OS, it would ask for a username and password. The default for Hexxus's image is facepunch/facepunch. That is for the initial offline login, if you have internet connection you can try it with your usual gmail login.
Navigator - It is fairly easy to use the chromium OS, as there is only a browser and some simple settings of the machine. Most noticeably is the use of the F8 command. This command shows a translucent version of your keyboard, and the shortcuts available when hitting any of the combination of
Have fun hacking.