For both the new (tiny) generation, and the last generation, what media formats and codecs are supported for streaming to Apple TV?
How does that streaming work -- is it all iTunes-based, or are there other ways to go about doing it?
The original Apple TV (out of box) preferred to treat your Apple TV like an iPod. It wanted you to sync your video from iTunes and had the following limitation:
The new Apple TV has identical requirements as that of the new iPod touch and iPhone 4:
As for how it works, while nothing hard has been released from the UI screenshots released items from the internet (iTunes store, YouTube, Netflix, etc.) will stream from their respective sources while your photos, music and video streams directly from iTunes or from an iPhone, iPad or iPod touch (via AirPlay coming in iOS 4.2)
according to Wiki Apple TV support:
and for audio Codecs: