The comments app is just an example I suppose, could be any content type.
So, bearing in mind I'm no guru ....
1. In my content type I would have a form field which would show my ratings content type
2. In my content type I would have a list field which would show a list view of the current rating for this piece of content
3. I would have only the button visible for my ratings form so that they can submit the ratings form
5. I would probably do what designbengel/coolcat creations did to get average value for my list view
Is that the idea?