I am ... FAIRLY confident in saying that Civ IV AI is not programmed to treat the human AI any differently, it is actually human psychology that makes it seem the case. If you learn to copy the behaviors of the AI, as opposed to acting as you have previously ... you will generally make good AI friends who might even gift you techs, etc.
Once an AI even offered to be my vassal during an MP game. While this has happened many times in single player games, it came in quite handy this particular time.
Regardless, it seems that the AI only favors strength, and as soon as it sees a weak element all AI will unite in dividing the spoils of the weaker player/AI.
Also, if you have come to power by stepping on AI's toes and not acceding to their demands, even if you are powerful the AI will not respect you.
In any event, whenever ANYONE has a monopolized hegemony (be it player or AI) and is starting to "divide" and conquer his enemies rather aggressively ... it is at this point that his fractured, vastly smaller rivals need to "unite" (whether human or AI) against the large aggressor, that they may at least carve some of their own empires out of the aggressor's territory, and thus balance the field ... and once the large aggressor dips below 2nd place .... alliance members start to drop out of the alliance and once again pursue their own individualistic goals.
It is the current AI, that tends not to band together, that makes playing the Infernals so fun "Weakling Humans, and your petty rivalries ... one by one you will fall into the ever-growing fold! Muahaha!!"
The Idea being that the AI look after their own interests so solely that they never band together to stop a world-encompassing monster Superpower. (IE my Infernal shadow upon the land)
I hope this helps with what an AI should know, how it should react