In past we had reported about Google Chrome OS. Basically Google Chrome OS is based on Chromium project which open source project that aims to build an operating system that provides a fast, simple, and more secure computing experience for people who spend most of their time on the web.
First working prototype of Google Chrome OS was demonstrated sometime back at Chrome event and the download links of compiled Chrome OS are already published on many websites.
If you have time & free space on your hard drive then you can download chrome OS and install on your machine but if you don’t want to install then USB version of Google Chrome OS might be helpful to you.
Guy over at carbon.hexxeh.net has build the image of Google Chrome OS named as Chrome OS Diet USB version. Which lets you to install Google Chrome OS on USB flash drive (requires only 1 GB) and boot your computer in Google Chrome OS using that USB drive.