Got the 0x80070643 error while trying to install version 4.7 of the software. Seems to be a common problem.
After trying many things:
1. Uninstall old version of Zune
2. Change permissions on “HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Installer\UserData\S-1-5-18\Components” to the Administrator.
3. Delete the Zune folder in the Program Files folder
4. Created the zune folder in the program files folder
The one thing that seemed to make the installer work was a system restart. Not sure if any of the above steps helped, but if you have the same problem, I would first try and restart the computer. If that doesn’t work, uninstall your existing Zune install and then restart and then reinstall. (imo: I think the problem probably stems from the fact that the installer is trying to install without forcing a system restart – sometimes a system needs to be restarted when attempting an upgrade – nothing wrong with that!)
I love the Zune, Windows Phone 7 platforms. But you would think that when Microsoft is trying to go after the Apple iPhone/iTouch market, they would better test the installer and also have some meaningful error messages that make sense to the masses (what in the world is 0x80070643).