The following applies ONLY with CSO's (Custom Scenery Objects) downloaded from the internet!
Go to C:/Program Files (x86)/Atari/RollerCoasterTycoon3(Platinum, Gold, Silver, etc.)/Style/Themed.
Then open the .zip or .rar file and there will be a folder inside. If you do not have a file that opens .rar files, go to
http://www.win-rar.com/website/index.php...=64bit&L=0 and download WinRAR. You never have to buy it, even though it tells you that you 30 day trial has expired. Just exit out of the pop-up box.
Put the two windows side-by-side and drag the folder in your download and move it into the Themed folder.
Delete the .zip or .rar file that you downloaded and open/re-open RCT3.