Last I heard, that Sally Hemmings stuff was unsubstantiated garbage.
http://findarticles.com/p/articles/mi_m1571/is_19_17/ai_75021627
http://www.freerepublic.com/forum/a3b1e31964372.htm
Try to official Jefferson organization:
http://www.monticello.org/plantation/hemingscontro/hemings-jefferson_contro.html