I downloaded Chrome OS Vanilla in vdi format. When I run Chrome OS in Virtualbox , on chrome the startup screen the third option is for setting up the network since my virtual machine is not connected to a network, I can't go to next step. I want to access system offline - how would I set up ChromeOS to run offline?
Chrome OS Vanilla can indeed be run offline, but you have to get past that annoying setup problem in Virtualbox. Your first objective is to get online because you have to setup and configure the OS for your account. Once you have setup Chrome, you can install all the apps you need and you will be able to use Chrome OS offline. I had the exact same issue as you when I wanted to evaluate the OS for use as a backup laptop. I downloaded the Vanilla .vdi for use in Virtualbox on my iMac and it took some trial and error but I was able to get connected and set up. Here is my setup for the Network settings that allowed me to get internet access.
You will now see "Ethernet" in the Ntwork drop down. You now have internet! Continue your setup and then go the Chrome store to install apps that work great offline. In the 2 years since the Chrome store came out, there have been a ton of apps that were written to work just fine offline. All of the Google Apps work fine offline, including Docs, Calendar and Email.
Here is an article I found that explains how you much success you can have offline with a Chromebook.
It can indeed be done. The others are simply misinformed.