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 order to solve this on my system, I cheated -- I copied the 64-bit executables (in \Program Files\IIS Express\) over the 32-bit executables (in \Program Files (x86)\IIS Express\). Visual Studio doesn't seem to care whether it's one or the other.
I guess we will have to wait and see if the final release of VS 2012 will allow for choosing between the 32-bit and 64-bit IIS Express.