With credit to http://nonsenseinbasic.blogspot.com/2009/04/google-earth-installation-solving-error.html
I recently tried to install Google Earth on my Vista X64 setup, so I could play with Geotagging photos - unfortunately Google Updater kept failing the installation. On an attempt to manually install, the installer bombed out with the mysterious error 0x80040905. Helpful stuff.
On my machine the problem was to do with mapped network drives.
First I checked this webpage for advice - it might help some of you, but it wasn't relevant to my problem as I don't have any existing versions of Google Earth installed. Then I remember an issue with some Adobe installations which had given me a weird 'Invalid Drive' error in the past.
The solution proved to be the same one:
1.Run CMD as Administrator. (type CMD into the start menu, then right click on the CMD icon in the start menu and choose 'Run as Administrator')
2.Type NET USE - you should see a list of any mapped network drives, but they will probably be listed as Unavailable.
3.For each network drive, type the command NET USE M: \\SERVER\SHARE replacing the server and share as appropriate.
4.Just for kicks, type NET USE again to check that your network shares are now up and running.
5.Don't close the command prompt just yet, install Google Earth and everything should go OK.
The reason for this is that in Vista network shares are set up on a per user basis, and the installer is running as Administrator. For more info do some sort of google search like this one.