Oh, now I see where Anthonius is getting at... This is a very simple trick of adding transparency instead of adding holes to the model or the texture. I suggest using Photoshop for this as I can't recall the equivalent in GIMP. Getting a mistake here is a result of overlooking any minor detail. 
You don't need to edit the main texture at all, no black spots there. All you have to do is simply make an alpha channel, and fill in the areas that you want to "erase" with black. In your case, you want to "erase" some holes in the front of the armor to make eyeholes.
Look at this GIF as a demonstration:
I wanted to make the cams (wheels) and the red dot sight without having to make a seperate model, so all I had to do was go into the Channels box, open the Alpha 1 Layer, selected the area that I wanted to "erase", and filled it in with black. The result is visible in the final screenshot.
If you don't have Alpha 1 in the Channels list, then click on the little paper called "Create New Channel", this automatically makes Alpha 1 for you. It will be all black, so just use the fill tool and change it into white. From there, you just add the black spots where you need them.
I hope this clears up some fog.