Also when installing downloads into ZT 1 Do Not use the ingame check locally feature this causes unnecessary files to be installed that when you want to remove downloads are difficult to locate.
Once you have the files extracted to the temporary folder you have open that folder highlight the file you want to install by clicking on it. If you have mere then 1 ztd file you want to install at the same time hold down the Ctrl key and click on all the ZTd files you want to install. With all the files highlighted go to Edit/Copy. now navigate to the dlupdates folder in the Zoo Tycoon directory and open it, now click Edit/Paste.
Always install your downloads manually.