You have to follow 3 basic steps and have a little bit of patience … and really, it couldn’t get any easier.
This guide is only to be used with a FIRST GENERATION AppleTV - i.e. the silver one, not the black one!
You need a USB pendrive of at least 4Gb – keep in mind that the drive will be COMPLETELY WIPED!
Insert the USB pendrive into a USB port of your Windows computer before proceeding (I did it in Bootcamp on a Macbook Pro).
You can download the zip file either from the StmLabs website (to make sure you have the most recent one) or download it here (see below).
Click the options “Native Apple OS” and “Internal Hard Drive“, check the correct device indicating your USB drive and finally click the “Go” button.
The application will now download the OS image (which will take a little bit) for your AppleTV and finally created and prepare your USB drive – follow the instructions of the application.
Power down your AppleTV (i.e. jank the cord). Insert the USB pendrive into your AppleTV and power the AppleTV up. During the startup of your AppleTV press “menu” and “-“ simultaneously on the remote to make your AppleTV take the USB pendrive as it’s boot device. Follow the instructions.
And that’s pretty much all there is to it and after a few reboots the AppleTV acts like never ever changed …