Hiya Sebastian,
You can use the tilemaps straight from RPGmaker2k which is bound to cheer some of you lot up, only reason i never mentioned it before is that most are rips or copyrighted therefore i cannot personally use them for the demo for legal reasons.
(my own tileset is coming along ok, its not amazing but it'll do the job)
As for the 'maker' side of things, I created Gigas-Engine two years ago for the PC so i have a good idea of how it should turn out, i am however rewriting all the code from scratch to best use the GP32.
just out of interest, here a couple of shots from the PC version..
You get two editors, an Advanced Editor which is a PC based peice of software, at the moment its very ugly and just 'functional' but will allow you to edit everything on the map. Rather than using scripting i use a method called hotspots - this means you dont need to type any script and instead just pick and mix triggers/results from a pre-set list - it does the same stuff, but means editing the game is easier via GP32...
which brings me to the second editor, which is just "Gigas Editor" - this is for GP32 and is a built in part to the Gigas-Engine player, so while playing a game - if you think a tree would look better somewhere else, or a the badguys need to be moved about etc etc you can enter editing mode and change it on the fly - if you want to create animations or such tho you'll need to use the advanced editor.
On-the-fly RPG making is fun, you can even make it up as you go along if you've already created/loaded all the animations and graphics into the game via the Advanced EDitor.
hope that explains it, and proves i've actually been working on it for ages