Is 768p good enough in a TV?

1080p is the absolute best HD you can get (aka full HD) . 720 is still HD, just not as good. You can never get full HD out of a 720p TV because the TV doesn't have enough pixels. If you were to set the xbox to output 180, the picture will just be 720. About HD ready, I don't know what that is, you might mean digital ready which means that it has a digital tuner in it if you use an antenna.