Create Your Own Lab Environment
Now that you have seen how to install a few virtual machines in Virtual Box, it is time for you to install some of your own. If you have a copy of Windows XP, you may wish to start with that one. If not, search for Windows 2008 Server and download the official ISO from Microsoft to use in evaluation mode during this course.
Also, if you want to find a few other good vulnerable distributions, I recommend checking out VulnHub.com. This website is dedicated to provide virtual machines as "challenges" for hackers and security professionals to test their tools and their skills.
After you finish this class, you can always go back to VulnHub to find new virtual machines to play with and keep your skill up-to-date!