How can I set up creatures on a map that will interact, and be observable. For example, I want to create a game where two animals may fight, and then the main player could watch the fight take place, could I set up a priority system that would set certain behaviors ahead of others? I also want them to roam the map, and have different reactions to different environments.
I'd originally left a comment about how this was too general a question, but then I realized that pretty much all his points except the fighting are covered by the kitten tutorial on the latest version of AngryAnt's Behave.
While an explanation of the concepts behind behavior trees is not appropriate for this site, and the links SpinalJack and Tetrad will get you informed about those, that sample project would be a great starting point. It shouldn't be too difficult for you to extend it for fighting.
Here's another Question on Robot Steering with some good points about creature motion in general (although not combat).
This is really outside the scope of Unity Answers. It isn't really even specific to Unity.
You'll want to get started somewhere else. Offhand a good resource might be http://aigamedev.com/
http://answers.unity3d.com/questions/1372/ai-programing-resources
Some answers on here you can search for with the AI tag