I have tested Google Chrome OS (aka Chromium OS) using a USB pen drive, or more precisely Chrome OS Lime by Hexxeh.
Since I like it I would like to install it along side of my pre-installed Windows 7, however, I can not see any installation entry within the system..!
My guess is that one could do this by simply
Fix a partition
Make the partition it boot-able somehow
Copy the content of the USB-stick to the partition.
Add the partition to the boot loader using e.g. EasyBCD.exe.