After availability of Google Chrome OS / Chromium OS source code, one of gdgt engineer able to make virtual image of Chrome OS. Now you can run Chrome OS on Windows, Linux or Mac by using VMware or VirtualBox. To run Chrome OS in Windows 7 follow these steps after a jump
Downlaod Virtual box x86/amd version click here
Install VirtualBox that you have downloaded in Step-1. Follow the installation wizard steps to install VirtualBox
Run the VirtualBox click on Start button > All programs > Sun VirtualBox > VirtualBox
This will asks you for the registration, if you want to get news updates about VirtualBox fill the form and submit or just click Cancel.
Click on New icon to create a new Virtual machine.
Click Next button to start virtual machine wizard
Type ChromeOS in the name field or type what you like, Select operating system as Linux and Version as Other Linux and click Next button (see screenshot below)
Select amount of memory to virtual machine like 256 or you can increase to 512 and click Next button
In the next windows select the Use existing hardisk radio button and click on yellow folder icon
Now its time to load Chrome OS virtual image that you have download and extracted in step-2, click on Add icon and select the .vmdk file.
Select the loaded virtual image and click the Select button
Click Next button and then Finish
Now you have loaded Chrome OS but its not strated yet, you need to click Start icon to start it and wait for few seconds to start Chrome OS.
Feel free to ask about any problem you are facing to install Chome OS in Windows 7.
See also how to install Chrome OS on Mac