The article covers the general gist of running an OS in Virtualbox, but…has a couple of gotcha’s that are worth watching out for with SteamOS. I like how they say you should give it a min or 4 GB of RAM. Its amazing how much CPU/disk/RAM/videocard games need.
http://www.howtogeek.com/224998/how-to-install-steamos-in-virtualbox/