Wow, that is very strange indeed. That's the standard Windows message when you try to run an exe that isn't 32bits (or 64bits) compliant. I assume you're running the x64 version of Windows? Is this error shown when trying to run the game, or the installer? If it's the installer, I suggest redownloading it: http://mirrormoon.org/news/2010/02/download_links
If it's the game... Well, I suppose let's start with: can you give me the filesize in bytes (real size, not 'size on disk') of the exe file?