I downloaded this to install and test since someone asked about it. There is no crack included so the game asks for the CD to be inserted. This is what worked for me.
Here are the steps:

1. The version on here is the original retail version so it's only 1.10. To update it, go [http://www.enlight.com/ze/] to the official game website and download patches 1.20 and 1.22. You need to install 1.20 first and then 1.22.
2. Google the words 'gamecopyworld zoo empire' and find the entry Zoo Empire - PC Game Trainer Cheat PlayFix No ... - GameCopyWorld. Go to that page.
3. Download the first file called 'Zoo Empire v1.22 [ENGLISH] No-CD/Fixed EXE'.
4. Extract it after downloading and copy the ze.exe to where you installed Zoo Empire.
5. Enjoy your game~