Normal Map advice needed

[TSM]

I have a model that has alot of nuts on its frame, I plan to upload to Giants Hub when I have completed it, my problem is the nuts need to be part of the normal layer and removed from the model as per Giants guidelines I have tried making a normal from my diffuse using normal map plus in paint.net, but the nuts don't show up, I have a feeling I need to do it in Blender instead, but does that mean I would need to bake a new diffuse and specular in Blender aswell ?

Any advice would be appreciated been trawling the net and most of the information seems to be out of date or for photoshop.

TSM

Tried both paint.net and gimps normal plugins.