"Atheism, in a broad sense, is the rejection of belief in the existence of deities. In a narrower sense, atheism is specifically the position that there are no deities. Most inclusively, atheism is simply the absence of belief that any deities exist. Atheism is contrasted with theism, which in its most general form is the belief that at least one deity exists."
"The term atheism originated from the Greek ἄθεος (atheos), meaning "without god", which was applied with a negative connotation to those thought to reject the gods worshipped by the larger society."
Basically, Athiests don't believe in any sort of Higher Power (not to be confused with Agonistics, which don't believe in organized religion, but believe that there is a Higher Being, even if it isn't neccessarily God).
So, yes, we think the theory of Creationism is whack, and we believe in Evolution.
It all comes down to having scientifical explanations for most things that most people believe to be the work of God.