Me being the fan of 64 bit operating systems, I discovered an issue when working with Sitecore today. In particular I am running Windows Vista x64 Ultimate. After first discovering that the installer would not work, I performed a manual install. After I got everything manually installed, I attempted to run the site only to find an error stating that my app is not a valid win32 application. It was a BadImageFormatException (Exception from HRESULT: 0x800700C1).
After a little googling I discovered this was 64 bit related and the fix is to force IIS to run in 32 bit mode. To do this, you use adsutil.vbs. The syntax below will make it work.
cscript %SystemDrive%\inetpub\AdminScripts\adsutil.vbs set w3svc/AppPools/Enable32bitAppOnWin64 1
In the case of Sitecore I am guessing that one of their 3rd party DLLs wont run in 64 bit mode. No idea which one. I of course found nothing on their site or in their forums, so hopefully this post will be of use to another Sitecore developer down the road.