It used to be possible by converting the component output of the AppleTV to a RGB signal (these types of converters can be bought for less then 100 euro).
But I am not a 100% sure because I recently read some comments on the internet saying that the appleTV adds a signal to disturb this conversion. Solutions seem to be downgrading the AppleTV firmware.....
But as said: All this information is not from own experience but from reading on the internet (what led me to the conclusion to wait until I have a tv with component or HDMI input before I bu a apple TV).
Good Luck,
Bieele