It's not hard to call lua. Other stuff is probably more difficult, you use io.lines or some such, I don't really know anything about it.
But for lua you use:
Code:
dofile("folder.rte/filepath/script.lua");
You can also use require (not sure how the filepath works there) which I gather require is faster than dofile but limits the reloadability of the script (at least in the case of the ai).
With that you can call functions or variables defined in any lua file as if they were defined in this one. It's a great way to separate things into manageable chunks (e.g. my current scenario project has 7 separate lua files for the scenario so far).