I think what is important that if you want to get a wireless one you need one that has a USB adapter. The ATV doesn't have bluetooth so Apple wirless ones would not work, maybe if you find a Bluetooth USB plug that emulates a USB wired keyboard.
http://forum.atvflash.com/viewtopic.php?f=9&t=2725
BS9000, BS2300, BC2, BL2500, BL3, Bl2, BS1, BV8, BC4, A8