Hmm, i did a new fast teste, and something seems defenetly wrong with this :S not sure if it is some settings or if i am missing something here :S again, i know litle about this, only some theory i had from a course i had taken and some video tutorials :S
below i attached a render with mental ray a render with maya software, and the normal map.

Suposedly the mental ray should have the best result right? still the maya software has the more aproaching result to the real one. I mean, the mental ray does have the best result, from what i have seen on the normal map, but then again why did the normal map came out bad? :S the map shows only an extruded form going out of the face of the cube instead the real thing right beside it. i checked all the normals directions and they are correctly facing away from the model.. there couldnt be a mistak in, my opinion, from a fast extruded cube.