I've gotten it fully installed in Parallels, but the OS is limited to nvidia graphics cards, so currently all you get is a blank screen. I was going to put a full guide together, but it'll have to wait until it'll work properly. Note that the virtualbox guide is only part of the story- they've only gotten as far as installing Linux from the SteamOS image (which I've done with parallels), which is not the full SteamOS experience.