Zoo Tycoon Mac?

It appears to be only for Windows, not surprising since the games are published by Microsoft. So you'd need to run Windows on your Mac to be able to run the game.

By the way, it helps people help you if you have the correct information in your profile. Your current profile says that you are running Mac OS 8.6 or earlier, operating system versions which are many years old. Please change your profile to correctly reflect your current model of Mac and the version of Mac OS X its running.

Regards.

Here's an overview of the ways you can do this:

http://www.macwindows.com/winintelmac.html

All of the methods other than Crossover require you to have a valid license for Windows.

Regards.