SteamOS 1.0 Beta Download

Build your own Steam Machine
SteamOS Beta is the first public release of our Linux-based operating system. The base system draws from Debian 7, code named Debian Wheezy. Our work builds on top of the solid Debian core and optimizes it for a living room experience. Most of all, it is an open Linux platform that leaves you in full control. You can take charge of your system and install new software or content that you want.

Installing and Customizing SteamOS
What are the SteamOS Hardware Requirements?
Processor: Intel or AMD 64-bit capable processor
Memory: 4GB or more RAM
Hard Drive: 500GB or larger disk
Video Card: NVIDIA graphics card
(AMD and Intel graphics support coming soon!)
Additional: UEFI boot support
USB port for installation

How do I install SteamOS?
There are two different installation methods for SteamOS. The recommended method is the Default Installation method, which is a pre-configured image-based install using CloneZilla. The other method uses Debian Installer, which allows for customization after an automated install step. Please choose one of those methods below.


WARNING: Both installation methods will erase all content on the target computer

Default Installation
You will need to create a SteamOS System Restore USB stick to perform this install. The image provided here requires at least a 1TB disk.

1.Download the default SteamOS beta installation
2.Format a 4GB or larger USB stick with the FAT32 filesystem. Use "SYSRESTORE" as the partition name.
3.Unzip the contents of SYSRESTORE.zip to this USB stick to create the System Restore USB stick.
4.Put the System Restore USB stick in your target machine. Boot your machine and tell the BIOS to boot off the stick. (usually something like F8, F11 or F12 will bring up the BIOS boot menu).
5.Make sure you select the UEFI entry, it may look something like "UEFI: Patriot Memory PMAP". If there is no UEFI entry, you may need to enable UEFI support in your BIOS setup.
6.Select "Restore Entire Disk" from the GRUB menu.
7.When it is complete it will shutdown. Power on the machine to boot into your freshly re-imaged SteamOS.

Custom Installation
The second method is based on the Debian Installer. It requires multiple configuration steps:


1.Download the custom SteamOS beta installation
2.Unzip the SteamOS.zip file to a blank, FAT32-formatted USB stick.
3.Put the USB stick in your target machine. Boot your machine and tell the BIOS to boot off the stick. (usually something like F8, F11, or F12 will bring up the BIOS boot menu).
4.Make sure you select the UEFI entry, it may look something like "UEFI: Patriot Memory PMAP". If there is no UEFI entry, you may need to enable UEFI support in your BIOS setup.
5.Selected "Automated install" from the menu.
6.The rest of the installation is unattended and will repartition the drive and install SteamOS.
7.After installation is complete, log onto the resulting system (using the Gnome session) with the predefined "steam" account. The password is "steam". Run steam, accept the EULA, and let it bootstrap. Logoff the steam account.
8.Log on with the "desktop" account. The password is "desktop".
9.From a terminal window, run ~/post_logon.sh. This will prompt for a password - enter "desktop". This script will perform the post-install customizations, delete itself, then reboot into the recovery partition capture utility.
10.Confirm "y" to continue and the recovery partition will be created. When it is finished, reboot into your freshly installed SteamOS.



FAQ
SteamOS FAQ :: Steam Universe

Source
SteamOS

 

I'm waiting for AMD support before I use it. Kinda odd they didn't have these supported on initial beta release.