A hacker named Turbo has posted instructions on enabling USB keyboard and mouse to work with the Apple TV. To do so, you need to download the patch he has written, and then apply it to your mach_kernel.prelink file with this command:

bspatch mach_kernel.prelink mach_kernel.patched turbo-disable-usb-whitelist-20070330.bsdiff

You can then use this tip from AwkwardTV to enable your mouse pointer (which you won’t see otherwise), and you are away!