Zune PC app is main use Nokia WP OS phone’s PC synchronization tool, so Nokia Lumia phone can use Zune PC apps to sync PC. You can get below function after using it, your phone can sync video, picture and music between Nokia Lumia and PC, upgrade Lumia phone fireware, sync WP’s shop software in PC. If you discover your sync picture is bad, you must set to forbid Zune picture compression.
The link has the download Zune.
We know the latest firware for Lumia 800 is 7.10.8773.98, you can upgrade using Zune.