A USB patch was released on Friday enabling you to use your USB port on your Apple TV to hook up to an external hard drive. Right now it only works with Apple TV Software 1.0 (and not the current 1.1 which has the YouTube upgrade/update).
Here’s the list of what you’ll need:
1. An ssh-enabled Apple TV
2. One installed version of Mac OS X 10.4 Intel
3. An Intel Mac or Intel-based Linux/Unix system to run the script which will patch the kernel on the Apple TV remotely
4. An unmodified copy of the ‘mach_kernel.prelink’ file from the Apple TV.
5. One external USB drive formatted using “Journaled HFS+”.
Apple TV
For the rest of what you need click check out Appletvhacks.net