Turn your Apple TV into a Boxee Box with the new Boxee Beta.
Previous versions of Boxee allowed you to install the media center software on the pre-Apple TV 3.0 OS, but you can install the new beta version of Boxee on your Apple TV with the latest OS.
Thanks to a bit of hackery, you can now install the latest Boxee beta on your Apple TV with OS versions 3.0 and 2.4. The Boxee beta is the same software we expect on the Boxee Box shipping this summer.
Boxee has posted a full guide on how to complete the installation on your Apple TV, however, it is not for the non-techie. You'll need to SSH into your Apple TV and mess around with the Terminal to get the software installed.
Be sure to check the comments on the Boxee post if you're using a different ATV firmware version before attempting to install. Several users have tried the install on different versions of the ATV firmware, and are posting their conclusions.
