Question about co-op

Hey, just started playing Napolean again after a year or so. I was wondering if it is possible to set up a custom battle where I can play with a friend (an army each) against the AI. Or can we setup a multiplayer battle and fill the two enemy slots with AI players?

I believe you can play against AI armies in custom battles through multiplayer or play the cooperative Spanish campaign. Best option is to test either and see what works out.

Yes if you are talking about multiplayer battle you just host a game in the multiplayer area and then set a password, make the changes you want(AI, difficulty, map, rules, etc.) and invite your friend.
If you are talking about multiplayer campaign you can play coop, sort of, that is if you are allied in-game and attack cities side by side, thus allowing you to reinforce each others armies. I hope it helped! If not you can post a message on my wall if you have any questions, or here.

to win a MP campaign in Napoleon, you have to take the other player's capital if i remember well. In italian and egypt campaign you are enemies at the start