No you cant, Didnt really know UT had a 1st player :haha:
Well you probably could but it's a Mod and not a actual add-on that came with the original game
If you were to play Co-op you'll need a Game Pad so your friend can play with the same computer
You can play some of the included game modes like Onslaught (my fav), Assault, or Team Deathmatch with your buddies over a network/internet, but not really sure what you're asking. Need a few more details about what you really want.