most people here are wrong, and simply put this is probaly one of the biggest misundertaandings when argueing religon.
atheism and agnosticism are not mutaly exclusive, since they refer to differnt things.
atheism:, refers to belife or more acuratly the lack there of, the broadest definition being someone who lacks a belife in gods or dietys.
thesim:refers to belife in a god.
agnosticism: refers to KNOWLEDGE , they don't know wheither god exsit's or not.
therefore you can be a both an athesit and agnostic, or a theist and agnostic.
an atheist/agnostic dosen't belive in god but dosen't claim to know he dosen't exsit.
an theist/agnostic belives in god but dosen't claim to know he dose exsit.
hope this clears some of this mess up