Different Page templates

I need to create both page and post templates that will allow me to show different ads and sidebar content depending on the type of page or post it is.

And I need for the different templates to be shown as options in the creation or even editing phase, in the dropdown. I was able to do this using the Proximity theme, but because Atahualpa uses just the one index.php file, I can't figure out how to do it.

Help!