You shouldn't have a problem with having two few CDs. However you might have a problem, depending on the way you set up your network, joining other MP games.
If you have seperate IP addresses you be able to play fine. But, if you are both sharing one external IP address, you will not be able to join the same MP game. You can join seperate games. To play in the same game, one of you will have to host, having the other join using the internal IP address. One of you will not be able to chat with anyone but the host...... it works...
noxian