Someone posted over on HBO a link to a Windows 7 theme that includes, you guessed it, screens of Halo: Reach. It also comes with sounds from the game, but no screen saver. You can find it on the main themes page or download it here.
Halo 5: Guardians
Halo 2 for PC
Get ready for our upcoming Halo 2 night on PC. Grab Halo 2 for PC today!
Or check out the Halo Store on Amazon.com.