Wouldn't you just call that something like "no-god-ism?" Perhaps with a latin translation?

Well, "no" would be "a-"

"-theism- actually contains two roots: -the-, meaning "god, divinity", and "-ism", which is a suffix used to create abstract nouns denoting a actions, conditions, or beliefs." - http://wiki.answers.com/Q/What_does_the_root_theism_mean

So "athe" would mean "no gods", and "atheism" would be that belief.

Which is a long-winded way of saying that, um, atheism already is the correct term.

I also learned that "athe" is a fun word to say ^_^