Well once upon a time you could use crazy bump to do all normal/specular/etc maps for textures but that's had its format changed and now you need to actually pay for it to use it
After compiling the textures, here's how it looks in-game:
EDIT:
So, I revised the texture a little, following the advice given in comments on this thread; mostly rounding off the normal map edges, and adding some brush strokes:
And if anyone's interested, the PSD is available (7zipped, 18MB).
If you've got any questions about the details of a particular step, please ask.
How did you round off the Normal map?
How did you keep the edges detailed?