This sounds like a very worthwhile project Stickgrinder. Just a heads up though, to my knowledge no one has yet been able to convert Tear's Saderan Tutorial to GIMP. The tutorial involves using certain features (i.e. layer styles, layer groups, brush styles) that GIMP simply lacks. While there are ways around some of these issues (e.g. there is a layer styles plugin for GIMP), I've not found any way to replicate anything remotely close to the brush presets (bevel & emboss, drop shadow etc) that are required to product features of the landscape in Tears tut. What I'm saying is that either you need PS for this map, or you might want to try a different style of map. Best of luck though.