When I download custom scenery what folder do i put it in? and where do i find it in the game?:/

Step 1. Where I download to?.

Just download to desktop and move to *Drive Letter*:\Program Files\Atari\RollerCoaster Tycoon® 3\Style\Themed

or direct to this 'Themed' folder.

Step 2. How to extract the ZIP or RAR file.

Extracting the ZIP archive is possible in Windows XP, by Open this Zip file by double click to open, then click 'Extract all files' the left side menu of explorer.

With WinZip installed, it is also possible to extract the contents of a ZIP archive file.
To begin, right mouse button click on the ZIP file and extract here.

With WinRAR installed, it is possible to extract the RAR/ZIP archive.
To begin, right mouse button click on the RAR file and extract here.

With WinAce installed, You can extract the many type inc ZIP archive.
To begin, right mouse button click on this archive and 'Extract to...'

If you dont have WinZip or WinRAR
WinZip
WinRAR

Other programs you can use with ZIP or other compession file.
www.powerarchiver.com - free
www.picozip.com
www.winace.com

If this custom scenery pack is EXE file, then you dont have to worry to extract.

Step 3. How to stop the SID error or crash my game?.

IMPORTANT CHECK THE FOLDER
If this folders aren't right in structured, then you will get the error.

Open this folder you have extracted/installed and you should find a folder (or sometime there might have more than one folder like DRP's lightz pack) and two files with the style ovl extension. If error, then move to the right structure.

Once it is working, You may can delete the ZIP RAR or EXE of custom scenery or save it as backup.

This is from iceatcs, Atari Forums.

As for in-game location, you sort of have to search for it. Usually the custom scenery set will be located in the structure/building tab (I think that's what it's called).