Well, today every BG2 mod is made with WeiDU.exe, that is the renamed setup-*modname*.exe you use to install every mod one way or another. Well unless you use automated tools ... but that uses weidu too. That file reads the setup-*modname*.tp2 file from the mod folder. The .tp2 file is just a weidu instructions file that tells what the .exe needs to do. Itself is just a text file with commands on it. And if you use Windows, you can make it with Notepad and get a kick to it.
Now all the code you'll put into it has a very large readme library in the weidu's actual support site, via PPG, here. And it's also distributed there, in the archive. The latest version.
The readme is a ... way too large for anyone to know completely, well... at least for most mod makers, and then there's even the part where people add things into it.
That's the quick clanse of things. Now, you first have to deside of whjich game you want to make the mod for... well mostly. Then what it's about... it's generally recomended that you first try to add an item. Just one... you can pick things up from there and make more after you know you can do things.
As that helps ... and remember that you are not alone in this and yes the forum might contain things you could search, people can also guide you to find a good version of a useful examples, so don't be afraid to ask. And then the time was 1:53 AM, and I had to go to sleep... 
Yep, Jarno Mikkola. my Mega Mod FAQ. Use of the BWS, and how to use it(scroll down that post a bit).
OK, desert dweller, welcome to the sanity, you are free to search for the limit, it's out there, we drew it in the sand. Ouh, actually it was still snow then.. but anyways.
