Can an AppleTV wake a Snow Leopard Mac for playing back iTunes content? Is it possible to have an Apple TV wake a WiFi connected iMac running Snow Leopard for playback of iTunes content?

I vaguely remember a new revision of the AirPort routers supporting this through Bonjour Sleep proxy, but I couldn't find real details on this on apple.com, other than a support document. I couldn't quite follow the final flow from the users perspective.
You have to setup your mac to wake from sleep on the wifi. It all depends on the model of your machine whether its capable of doing this or not. You can read more about setting this up on your mac at the following KB article at Apple. 

http://support.apple.com/kb/HT3774