on x64 Windows 7 I am trying to get hello world MVC 3 website running as 64-bit process (so Environment.Is64BitProcess returns true on a page) using IIS Express 8 latest bet
In the registry, go to HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\IISExpress\8.0\InstallPath and change the path to the 64-bit iisexpress.exe location.