Thanks for the comments guys, the map was done 100% in basic paint.net with no plugins.
I basically created one black and white image which was split into two opposite images, one of the water, and one of the land, and then layered effects on them independently. I mostly used the rendered clouds to create textures and then put colored overlays on them. I don't think I could recreate another one exactly as I cant remember all the different overlays and such. There are at least 15 layers.
I'd really like to know how I can do patterns (like textures in Gimp) and bump maps.
Anyone know of a tutorial for this stuff?