Jailbreak – Tethered

AppleTV 2g – 4.4 (iOS 5)  – 4.4.2 (9A336a)

Jailbreak – unTethered

AppleTV 2g – 4.3 (iOS 4.3) – 4.3.0 (8F455)

Install onto Apple TV 2G

XBMC

Links

Where to Download Apple TV Firmware files (Restore links)