If you have downloaded Chrome OS and are wondering what the username and password are, here is a quick hint. Chrome OS allows users to login to the OS using a Google Account.
So in order to login to your account, just enter your Gmail username and password. The good thing about this is that you will be able to access Chrome OS using different IDs and no one else can access your applications or data.
Another thing to note is that Chrome OS stores everything in the cloud, which means that you no longer need to have huge hard drives. However, there is a very bad thing about Chrome OS, if you have no internet connection, you will be virtually locked out of your computer.
So it makes more sense to have Chrome OS on a dual boot or to run it on a virtual machine.
Please Note: For your own safety, create a new Google account, if you have downloaded a Chrome OS version using torrents.