I would recommend reposting in the correct forums for that, there is one specifically for AppleTV.Also you do not need OS X at all to use an AppleTV however my guess is you are referring to the AirPlay feature set. Please carefully read:
please click the link I provided earlier, you will see AirPlay will not play on a Late 2006 iMac. There is another application you can get whose name escapes me, however someone else may remember. I don't know if even it will work on your machine.