Well, with regard to general principles in eventing, scripting, and mapping, there is virtually no difference between XP and VX. Picture lighting, for instance, which is what you are asking for, is the exact same in both - you could learn the relevant principles from a tutorial made for RMVX as you could for one in XP. So, it actually makes it easier to find things since you have a greater variety of tutorials to choose from and nobody has to duplicate tutorials for every maker. Where there are major differences, such as in actual event systems and actual scripts, then it makes sense to separate them and we do.
That said, there are tutorials that are limited to one maker, and so there is a slight navigability cost, but given that it gives access to a greater variety of relevant tutorials for all your needs, I would say it is far better than the alternative of separating the Tutorials Database artificially into RMVX and RMXP.
Anyway, your question has already been answered - just make a stationary fog graphic that lightens the areas where there is a light source and darkens the areas where there isn't.
I don't really know what technique you are referring to when you say "transparent picture that makes most of the map darker," so I'm not entirely sure how that will interfere. But either it's a flashlight type script, in which case it can just be a picture with the add blend type, or it's a very similar fog technique and you can just adapt that graphic.