How to install Windows Live Messenger/Mail/etc... when you have problems...

Actually, I have experienced this problem too. Except it was when I was REINSTALLING WLM 8.5

This is what you do:
Go to:
C:/Documents and Settings/All Users/Application Data (in XP)
or
C:/ProgramData (in Vista)
and delete following folders: "WindowsLiveInstaller" and "WLInstaller".

Next, go to:
C:/Program Files/Windows Live (for XP and Vista)
and delete the "Installer" folder.

(remember to show hidden files before doing any of this)
Once you do that, you SHOULD be able to install WLM 8.5 with no problems.