I've had a bit of a read and had no luck, i'm running 4.0 (Under "About") which according to this post http://forum.firecore.com/topic/3418 means its actually 4.1. Installer is all good right up until it wants to transfer the files and says..
"Sorry, the installer could not connect to your AppleTV. Help!"
It shows up in the device list, i've also tried rebooting the appletv but same thing, Have i missed something obvious?