Newbie question about custom Races

[DavidG]

I've been messing around with a downloaded StarTrek mod and was hopping someone could tell me how the computer selects races for the AI races. ie If there is a folder in the ..\Pictures\Races folder is there a chance the computer will select that race? Does it need or use an .emp file? I also noticed that in the mod I downloaded some of the races had only a fraction of the pictures the default races have. Does this matter? or will the computer just replace the missing pics with default ones? Thanks in advance for any replies. This forum is great for answering questions that have no doubt been asked many times before!! Also if anyone has any sources Online that will give some tips about making modifications I'd appreciate knowing them. (although I gather this is pretty much a trial and error thing)