Genuinely curious, I have zero programming experience and I want to hear from the experts how challenging it actually is compared to other games. I understand basic technical terms but if you could explain the processes in ways someone that has little programming experience could understand that would be helpful as well. Also side-note I've been lurking here on and off over the years and am very glad to see the community is still very active, Long Live Arcanum!
There's plenty of good articles and there's still some knowledgeable people around. I've only ever worked on creating new modules, not making actual mods, but I found this was a good start: http://terra-arcanum.com/amtut/amtut.htm
If you want to mod the campaign you will need to extract the module the way rroyo and Shiin did, then open it in WorldEd. After reading AmTut, which is almost mandatory to avoid problems/surpirses, you should be able to mess arround with Arcanum Maps. Dialogues and Scripts are probably the hardest thing to make but you can produce any kind of content modification/additions within minutes.
Thank you both for your quick replies! I will look into the link and read about it when I have more free time.