google 'universal binary'
Since the game is older than all intel macs, it was originally designed to only run on PowerPC macs. There is a possibility that there could be a patch for the game to make it universal binary, allowing it to run on intel macs as well as PowerPC. I believe the game was ported to the mac by a company called Macsoft, so to find out if a patch exists, I'd start by looking on their site.
There is a possibility there is no patch for it, in which case you need to use a program called 'Rosetta'. This used to be installed by default on all macs until 10.6, but I think it's still available on the Mac install DVD.