So I'm going to make myself a GUI system and I was wondering which libraries I should use. I want it to be able to change themes and orientations of windows and such, along with being able to change the primitives like buttons in a script/cfg file. Should I use Lua or is that more complex than what I need? I've also been debating switching to Allegro 4.9 for speed reasons. Can 4.9 render models, or is there a way to insert direct OpenGL into it? Thanks for any advice you can give .

I also recommend keeping it simple. Also, if you are only going to use this in allegro at first, you can save some effort and make use of much of allegro to implement something good enough, but more importantly both highly usable and easy to write.
You are going to have to write those widgets anyway, so you may as well have a .c file for each one and use allegro functions on it's private BITMAP (which might be a sub bitmap of it's window's bitmap) at render time or something like that.

All that I am saying is a easy, working gui finished yesterday is better than worrying about making super-portable Yet Another GUI that you're still messing about with next Thursday. That's the method that I took with mine, and I'm not ashamed at all

It uses Direct3D or OpenGL, so you can render 3D models, but Allegro doesn't provide any routines I know of. There's even one example in the Allegro SVN that integrates it with Ogre, though I think it's not working right on other platforms ATM.

Yeah I guess that that would be pretty cool, if someone actually did it.