The main problem is they seem to have put it on a single server instead of the Steam CDN and now no one's able to download it
wget http://repo.steamstatic.com/download/SteamOSInstaller.zip
But it's choking every percent for me, so I doubt it'll finish.Use another VM or nix install to grab the zip, extract it to a path and run the following:
genisoimage -o test2.iso -r -J steamos/
(assuming you extracted the zip to steamos/)I've edited this post to remove most of what I said, the installer as it stands now is designed to work on UEFI compatible systems only and VirtualBox isn't compatible enough.
I'm not sure I can be bothered fixing it as the SteamOS TOS forbids distribution of modified versions.
You said you got partway through the installation -- did it finish successfully?
Wait, what? How does that work, vis-a-vis the GPL?
"NVIDIA graphics card (AMD and Intel graphics support coming soon)"
I believe VirtualBox emulates a graphics card, and not an NVIDIA one, so it may not run even on machines with an Nvidia card.
Using a real NVidia GPU from within a VM is possible, but not with VirtualBox, and not with most gaming systems (due to either having necessary hardware features disabled on overclockable Intel CPUs, or AMD systems lacking a second GPU for the host).