There are many ways to do this, and all of them are called
STEALING.
download free roller coaster 3
You can download it here: http://download.cnet.com/Roller-Coaster-Tycoon/3000-7551_4-10026882.html for a 40 minute free trial and then you can purchase it for $20.
The internet
Nope
iso hunt or sumotorrent
yes
games4theworld.org
i'm not sure about online but you can download a free trial on loads of websites
In a magical place where unicorns fart frogs and burp rainbows.
yes, type in on google or yahoo, etc 'RCT 3 download' and find a trial and download it
there is not really that are out there but you can get a demo online
You have to buy the game where ever you try to get it.