Well first, thanks for the compliment. I see myself as more the vocal minority in here anyways
The terrain editor is for building maps (hills, water, bases, etc). For skin editing you just need a graphics editor that supports layers (photoshop, gimp, paintshop pro, and others).
In theory it's easy. You just draw the layers so that when you save it out it looks like an airplane. You use the default skin for any given plane as the template and draw layers on top of it (but not drawing directly on it).
