This seems like a pretty good tutorial here, although you can skip the bit about making an AO map since you already have one, although it might be useful to give some of your details a little more of a 3D feel
Photoshop: AO and normal maps from a height map tutorial - UDK Developer's Group - Mod DB
This one here may be useful too:
Creating height maps for bump mapping
I mainly make my normal maps from High Poly Normal Bakes so I don't have that many examples to hand but one small example of a HM I made was for the plate that holds the rear thins for the
Blowpipe Missile I made.
I did most of the normal details on this missile with a high poly normal bake:
But this didn't turn out so well for the rear thin base plate so I did them with a HM.
Diffuse Texture & HM, then when I converted to a Normal Map And finally combined it with my HP Bake:
Its worth noting that this texture doesn't have that many details (some may argue it has waay more than it needs), since its only seen when firing, unlike your missile which can be seen on the hard points of a jet, which is also why the final textures for this blowpipe missile are saved at 64 x 256px (the promo shot seen above was shot in 128 x 512px).
So ye basically how a HM works is 50% white, or 128,128,128 RGB is a flat surface, 100% (255,255,255 RGB) white is something that sticks upwards really far, and 0% White aka, Black (0,0,0 RGB) is a very deep hole. So things like your rivets, its hard to see on the refs but it looks like they stick out very slightly, I would have them at around 60% White (153,153,153 RGB), and the grooves between each segment of the missile look to indent quite a bit, so I would have them at around 30% White (77,77,77 RGB), and other than that I think that's all you really need, then you just need to convert it to a normal and play with the strength of it till you get what you want
Hope that helps!
EDIT: Nice work on the Spec updates but it looks like the IR Sensor on the nose of your missile has now lost all of its details and I would say make it brighter too as you want it to really shine
