hi,
here a script that seem to be exactly what i want
http://wiki.blender.org/index.php/Extensions:2.6/Py/Scripts/Modeling/Solidify_Wireframe
unfortunally it didn"t work on Blender 2.69, so i am looking for a fix to this or a similar addon that do the same job .
i have also trioed it on blender 2.58 like mentionned in the wiki, but it gave me sricpting errors too
thanks and good day