HT1600: Apple TV (1st generation): How to update Apple TV softwareLearn about Apple TV (1st generation): How to update Apple TV software
Currently Being ModeratedOct 21, 2012 2:12 AM (in response to eholiday)
As SeaBeast said but you Mac needs to be mid 2011 for all models except MacBookPro which needs to be early 2011 or later.
Make sure you are on the same network, apple id and all home sharing is on. If that doesn't work reboot modem and Mac.
If you Mac is older or you run a PC try a third party app called airparrot.