FGBTTM Installation

Download an image (.iso) program such as PowerISO. http://www.poweriso.com/
Download the image file and extract it. http://www.poweriso.com/tutorials/faq.htm#open_iso_file
Run setup.exe and install the game.
After installation, open the game directory. Default is C:\Program Files (x86)\Family Guy Back to the Multiverse.
Copy all files from .iso's "SKIDROW" folder to the game directory.

The game is now cracked, but before you begin playing:
Right click "FGUY.exe" and open Properties.
In Compatibility tab, checkmark "Run program as an administrator."

Remember to use the saves found in the resources page.