Like gerard said, you need a scope, of what you hope to change for this mod, you need to know what your editing, where the files are, what they're called, something to edit them. You're in at the deep end IMHO. And you'll need something like a fuel gauge, otherwise you'll not notice, then all your hard work will have gone to waste.. And you probably need at least an intro to scripting, before you go messing with files...
UI though gerard would say this, but he didnt so... DONT FORGET TO BACKUP!