Use corflags.exe at the command line to see if it an .exe or .dll is meant to run only on a specific platform or under WOW64. You can also use corflags.exe to change the platform status of an .exe or .dll. See CorFlags Conversion Tool (CorFlags.exe) for more information. A Visual Studio assembly's CLR header (or COM+ Runtime header) has the Major Run-time Version Number set to 2 and the Minor Run-time Version Number set to 5. In Visual Studio 2003 assemblies, they are 2 and 0, respectively. All applications that have the minor runtime version set to 0 are treated as legacy applications and are always executed under WOW64 on 64-bit machines.
Alex S