I've had it with messing around with GL, for now

So I want to use sprites in jME.

I remember Mr Monkeycoder telling me about how to do this on the Javagaming forums but I don’t remember.

All I do is make a flat rectangle and then put a texture on it, but how would I use modulated lighting instead of vertex lighting?

modulated how? As in one set brightness across the whole sprite? If so, you can disable lighting on your Quad and set its vertex colors to varying shades of grey to control texture brightness.