Don't worry too much about the AI. Battlefront engine utilises shaders and is very much GPU bound - the CPU has hardly any work to do graphically. Missing skybox could be driver issues. I would suggest upgrading your drivers to the latest version, also ensure you are running DirectX 9.0c.
Tips to increase speed:
Crank down the FOV - field of vision (draw distance in other words)
Turn texture quality to low (this will stop the card choking so much)
Turn LOD (level of detail) to low
Reduce the resolution
Turn of Anti aliasing and Anistropic filtering if you have them on
Buying a new gfx card is always a good idea if you can afford it - but turning down lod and fov and turning the texures down should give you a huge increase in speed.