For starters you will find the Downloads link on the right side of the page under the affiliates list and the search box. You can click it in future to find the downloads database.
For now if you click this link
http://www.zooadmin.net/Smf/index.php?action=tpmod;dl=cat44 You will be taken to the animals area where you can click on the different categories to locate animals for download.
Once you click on a category a new page will open with a list of animals. Click on the animal name to reach the download page. Click on the download button. A files download will open. Click on save and then choose where on your system you want to save the file and click the save button.
Once you have all the files you want downloaded you can then look here
http://www.zooadmin.net/Smf/index.php?topic=2500.0 and here
http://www.zooadmin.net/Smf/index.php?topic=3607.0 to find instructions on how to unzip the file and install into your game. If you have any problems installing the files please look here
http://www.zooadmin.net/Smf/index.php?board=72.0 for answers to help you get the files installed.