Yes, the possibilities to mod are vast, and at the same time daunting. I guess it really depends on what the plan for your mod is. If you decide 'just' to make a new adventure for exsisting characters and stay in the same world, you can use most of the files that are provided by the Crown of Magis module. I mean stuff like monster_classes, items, and so on.
OTOH, if you try to make a whole new mod from scratch, you'll not only need skills in modding, but also project management
.
IMHO the best way to learn is to look at exsisting modules and mods (just like Henk suggests), re-use what you like and make some changes. This is the way that I started my mod, built on the Crown of Magis and it is still 99% of the original data files, while at the same time offering a new challenge, a new plot, and some new places to visit. And while it was never really meant to be a full-fledged mod (originally just a modding testing ground during the beta) or even publicly released, it has turned out reasonably well IMH(and biased)O.
Once you have started to get the hang of it and created a few new things, it becomes much easier and the abilitiy to re-use things is very handy. Just look at 'The Crack of Doom', it is fairly simply build, but at the same time a very nice module IMHO.
Certainly feel free to use any of the stuff that I created, if you like something of it. I have absolutely no problems of sharing my work. And if you have any more specific questions, by all means, ask them.
Hope that helps and have fun modding,
Rollo
[ April 17, 2003, 15:46: Message edited by: Rollo ]