The quickest legal solution would be to get the “Play the World” expansion pack. Then one of you could play with the Civ III CD, and one of you could play with the PTW CD.
It is a standard antipiracy thing. If you dont own the game(and have it in the drive) you won’t be able to play the game. Of course about 2 ms after a game is released you can download a nocd crack from …uhm some site. So all it does is annoy people.
Triton is correct, but it wouldn’t hurt to get the PTW expansion anyway - it’s a lot of fun multiplayer. Although, don’t get PTW, get “Conquests,” because it includes PTW. And adds more stuff to the game.
I recommend Conquests as well. I never play online/multiplayer, but it’s well worth it for the new civilizations and units it adds to the basic CIII game.