Poryhack said:
I know a guy who is probably at the forefront of pokemon map hacking and he says adding maps is not so hard as you would think. Basically just adding an entry to a table.
Depending on the forum he'll go as either Alpha or pokesplash.
Granted its not as easy as most think, its still dificult and requires a basic understanding of the games and hacking them. Anyways, I dont think a hack like this could be done on any generation before 4, simply because Gen 1-3 didnt have the map space for all 4 regions. Apparently Gen 4 does, but we dont know how to make maps for it, as far as I know.