Multi-Player against AI

[Mr. T]

Ok, I searched for "cooperative" info on the site and found bunches of stuff, but nothing I could readily understand. So here's the question. Is it possible to make maps (yup, I'm actually finally making some maps of my own) that allow me and a friend to work together (on my home LAN) to kill off the AI bad guys? We've been doing it via Deathmatch, but sometimes we run across bad guys who I can see, but my friend can't (or vise versa).

Another thing... I've finally got it set up so at the beginning of the game, I 'spawn' right next to my helo and I can jump in before it takes off. However, my friend has to wait to "join" the game until I'm loaded, and by the time HE gets in the game, his (or what is supposed to be his) helo has taken off and left him. Grrrrrrr!

Any suggestions? Am I going to have to live with only a Deathmatch kind of game?