How can I export tangent normals in blender to a .obj file? Mainly, how do I convert the mesh to tangents?

What do you mean ? Do you mean normal +tangent + binormal ? (used i.e. for normalmapping)
As far as I know .obj fileformat doesn't support tangent,binormal just a normal. But you could calculate from normal and texture coords the tangent and binormal, but this is independent from the .obj fileformat.

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Ashaman

Here are three great starting points for understanding normal mapping with Blender:

http://blenderartists.org/forum/showthread.php?t=138194

http://feeblemind.tuxfamily.org/dotclear/index.php/2005/08/23/43-tutorial-blender-and-normal-maps

http://vi-wer.de.tl/Normalmap-Tutorial.htm?PHPSESSID=21505d275ea4b17e7c94a51c8ff43dcb

Don't worry if it takes a while to understand it and then successfully create a good map. It's not easy stuff.

If I am to understand your question, the normal map is not part of a 3D file -- it is an image that is created from a 3D file (usually a high poly one) and then applied back onto a 3D file (usually a low poly one) as part of a material.

Scott

thanks.
I have create a coolda importer that get the binormal and the tangents ,but if i would to load the normal mapped mesh in my real time game , i can use binormal and tangents or i must create a shader and the blender's normal map exported as bitmap?