The Zi8 is a camera ... it is not a multimedia player.
The camera will only recognize/play video files or photo files that it creates.
I don't know of any digital camera that will function in the manor that you describe.
I have recently bought a Kodak Zi8 and I am struggling to put edited movies onto the SD card for the camcorder to recognise. I want to be able to play these movies on my HD TV. Does anyone know of a way of doing so? I am using OSX if that helps.