Configuration :: Confusion Deploying 64bit Website To Window 2003 R2 64bit?

Apologies if this is is in the wrong place but I'm not sure where this issue fits. My issue deals with setting up an ASP.NET 64bit website on IIS6 (W2003 R2) so it could be a compiling problem or an IIS setup issue - I've read so much now I'm all tied up in knots.I have a web app which has been written on top of my company's custom framework, both have been compiled in .Net 2.0 with the "AnyCPU" option and run quite happily on my laptop within Visual Studio 2008 (on a Windows 7 Enterprise 64bit laptop). All of the code is managed code with the exception of 1 3rd party dll that I think is still 32bit.

Question 1: when running on my laptop in VS, is my web app running in 32bit or 64bit mode, given the OS is 64bit? I have both versions of .NET 2.0 installed.I have a new desktop that is to be our test server, and has been installed with Windows 2003 R2 and had IIS6 configured (same as the production environment). Again, both versions of .NET 2.0 are installed. When I copy my web app to the server and browse to the site, I get the dreaded "%1 is not a valid Win32 application", and sometimes (depending on what settings I've been playing with) "Service Unavailable" messages. If I register the .NET version to 32bit, and set the IIS 'Enable32bitAppOnWin64' to true, the app runs happliy the same as when on my laptop......but I don't want it to do that! I want to run IIS to run in 64bit mode with the 64bit .NET 2.0 Framework!Question 2: What does IIS see to make it think that my app is a Win32 app or am I interpreting that message wrong? Is the fact that I have 1 32bit dll in the in folder enough for IIS to say "32bit" and keel over?

My understanding of the "AnyCPU" option was that as long as the code is all managed code within the application, the bitness of the OS does not matter so I cannot understand why IIS6 cannot run the app in 64bit mode....and no, installing IIS7 is not an option.