SteamOS is the first gaming Linux-based operating system. The base system draws from Debian 7, code named Debian Wheezy. More information, of course, available on website http://store.steampowered.com/livingroom/SteamOS/
I presume that you are here because you know what SteamOS is and you want to try run it as Virtual Machine in VMware Workstation on Windows. In few steps, I will show you how to do it.