I don't know much about 3D, but by searching the blender forums I've read something about some directX export options like "recalc. Normals"
http://forum.thegamecreators.com/?m=...ew&t=86821&b=3
and one export script:
http://blenderartists.org/forum/showthread.php?t=73602
and another one:
http://xoomer.alice.it/glabro1/python241.html