there is not really that are out there but you can get a demo online
download free roller coaster 3
yes
games4theworld.org
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
I'm not sure there is or not
There are many ways to do this, and all of them are called STEALING.
You have to buy the game where ever you try to get it.
iso hunt or sumotorrent
To play RCT you have to purchase it. It cannot be downloaded for free.
i'm not sure about online but you can download a free trial on loads of websites