GreenPois0n RC6 to jailbreak Apple TV 2G iOS 4.2.1 untethered is now available for download. Chronic Dev-Team has released the GreenPois0n RC6 for AppleTV 2nd generation, which provides untethered jailbreak for iOS 4.2.1 firmware.
Greenpois0n RC6 has been released for Mac OS X & Windows, which can now jailbreak iOS 4.2.1 on Apple TV 2G. With this released, Greenpois0n can jailbreak all iDevices including iPhone 4, 3GS, iPod Touch 4G, 3G, 2G and iPad, Apple TV 2G running iOS 4.2.1 firmware.
Also You Can See This Video Tutorial For Jailbreak Your Apple Device