The additional content created for Microsoft Flight Simulator X are constantly updated to support the newest operating system and the actual versions of FSX. In your case, the package (767 Captain (767-300 Base Pack) is available for installation on Windows 8. Just make sure to install it as Administrator to prevent any issues to happen. Also, make sure that you have installed latest Service Packs for FSX to extend compatibility between the base game and its add-ons.
