Check Your Temporary Files
If removing references to Google Earth in your Windows system registry didn’t solve the problem of how to completely uninstall Google Earth, there might yet be another chance.
Hidden somewhere on your PC will be a Microsoft installer file from an older version of Google Earth. By removing this file, you should then be able to complete installation of your preferred version of the application.
To find this installer file, you will need to locate your Windows Temp directory. In Windows XP this is usually c:\windows\temp – however you can confirm the actual location by going to Start > Run and entering %systemroot%\temp.
In this folder, you will find many installation and other temporary files used once only and then discarded by Windows. You can delete all of these, in particular the Google Earth.msi package, however you might prefer to take some precautions.
Once way to remove the files from this directory without deleting them is to create a new folder. Call it my-temp (or something equally meaningful) and then cut and paste the other contents of the c:\windows\temp folder into this new one. If everything moves without a problem, it is OK to delete the files. Anything that results in an error however will not be available for deletion at this time.
The Google Earth.msi file should be available to delete – one reboot later and you should be able to install Google Earth v5 without a problem.