Before we get into the installation, let's address the elephant in the room: Why use version 8.9 and IDE 1.8 instead of the newest versions?
Open Arduino 1.8. Write a simple blink sketch or a complex sensor reading script.
Proteus 8.9 SP2 offers a stable, robust simulation environment, while Arduino 1.8 provides a simple, reliable coding interface. Together, they allow you to simulate complex micro-controller projects before spending a dime on hardware components.