First I'd like to say what a great game this is.  I'm trying my hand on modding.  Hopeullay, I can get some help from all the great people here.  
First, how do i replace one of the current races in the game (example: replace the Thalian) with a custom one i'm making.  I don't want to mess up the current setting, so I was thinking of using the mod folder.  I already have the custom race image and logo.  How do i go about doing it?
Thanks