Unhacked AppleTVs will need to download aTV Flash 4.0.5 or version 1.0.b13 of atvusb-creator. Once installed on a USB flash drive, plug the drive into the AppleTV USB port and restart. The atvusb-creator install will also allow XBMC Media Center to run. Either way, hacking the AppleTV will give it new life — you may even dust the thing off. Here’s a more detailed install guide from the bloggers at Boxee.
By the way, Boxee will also run on your Intel-based Mac OS 10.4 or newer, Ubuntu Linux 9.04+ x86 only, and PCs running Windows XP or newer (x86_64 requires Vista or 7).