You don't mention if you have connected one mac to another. I have managed to play on LAN with 4 computers using only one CD key. However, I must add that in order to play LAN you don't need to have legitimate keys. I assume that you have a total of 4 different legitimate CD-Keys: 2 keys for Warcraft 3 and the expansion on one machine, and 2 keys for warcraft 3 and the expansion on another.
