I think this graph, from a Research 2000 poll commissioned by Kos speaks for itself.  The question's exact wording was: "Do you believe that Barack Obama was born in the United States of America or not?" No polling tricks, just a simple yes/no/unsure.  Obviously part of this is a partisan split, but there's an almost equal divide between the South (47 yes to 53 no/unsure) and everyone else (closer to 90/10) than Democrats (93/7) and Republicans (42/58).