AI scripting is pretty much standard if you want to mod, but I can understand you don't know (everone has to learn it sometime, right?).
Well, anyway, there's other threads about this. Rather than posting about it immediately, use the search function first. You'd be surprised how much you would find by using it, almost every question has already been asked before. So many newbies just post away about something, without searching for it first. You now know not to do that, so consider yourself enlightened.
I did some searching and this is what I found:
http://www.deezire.net/modules.php?n...ewtopic&t=6551
http://www.deezire.net/modules.php?n...ewtopic&t=6334
http://www.deezire.net/modules.php?n...ewtopic&t=4597
Is it possible to get the ai to use units you make yourself
