An ISO file is an image of the installation CD / DVD.
You will need something like PowerISO, or Alcohol 120% which are both software packages in order to mount a virtual CD / DVD drive and then install the game.
You may be able to burn the ISO image to a disk with something like Nero. Choose "File from Image".
When you can view the files in the image you must first install the game. Then within the image CD / DVD there will be a folder called "Crack" or similar that contains a file called rct2.exe. You must copy this file to your hard drive and overwrite the one that was created when you installed the game otherwise the game will not run.
This sounds a lot more complicated than it actually is, give it a go.