I was installing updates on a laptop running Vista x64. Mid install of updates it rebooted and then told me it was uninstalling some updates due to improper install of them. Which was fine. After the computer came back up I continued to install updates. Sadly I couldn't get Internet Explorer 8 to install due to it popping up the error "Setup cannot continue because a more recent version of Internet Explorer has been detected on this computer." I rebooted the computer and still had problems. I would usually ignore this but for other updates to show and progress I needed to get this to work.
I decided I would uninstall IE8 so it could re-install. After jumping into Programs and Features IE8 was no where to be found. So I then jumped online to see how to manually uninstall. Ran across a Microsoft Article showing the steps I had just checked earlier. No Go. They also showed a long command to run to get it to potentially uninstall the app. That didn't work either.
I then stumbled onto a forum post by "Chris Oliphant" on answers.microsoft.com. His post was my solution.
I downloaded IE8 for my version of Windows. Make sure you have the right version x64 or 32bit. I ran it and got the same error. Leaving the box open I browsed to the Root of the drive. You should a folder there with a long numbers and letters name.
Open that folder and run IE8.msu.(You may need to copy the files elsewhere if you run into issues) It will not check to see if IE8 or 9 are installed and will just overwrite the install of IE8 that is on the computer.
After it is done installing reboot the computer. You can now delete that folder that is at the root of the drive. (Be careful don't delete something else and mess up your computer) Re-run Windows Update and it should then find the additional updates. You are then good to go.