Source: Microsoft Support

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The question has been asked: Is there a 64-bit version of Visual Studio 2005 or Visual Studio 2008?

No.  Unfortunately, we do not have a 64-bit version of Visual Studio 2005 or Visual Studio 2008.  However we do support development and debugging of 64-bit application.  See below for more information:

With the introduction of the Visual Studio 2005, we are able to built applications for both 32-bit and 64-bit systems. The major advantage with the managed applications is that you do not need a separate version for each architecture as the Framework compiles that assembly to run on architecture of the operating system.

There is a requirement for building 64-bit managed assemblies and that is that all components utilized by the managed assembly must be capable of running on the 64-bit system.  For example, if an assembly need to call into a 32-bit COM component, that assembly must be compiled to target x86 CPU so that it runs under the WOW64 layer.

Visual Studio Development Environment 64-Bit Support:
 2005 - http://msdn2.microsoft.com/en-us/library/ms241066(VS.80).aspx (http://msdn2.microsoft.com/en-us/library/ms241066(VS.80).aspx)
 2008 - http://msdn2.microsoft.com/en-us/library/ms241066.aspx (http://msdn2.microsoft.com/en-us/library/ms241066.aspx)

Debugging of your 64-bit application is also possible from Visual Studio 2005 or Visual Studio 2008:

 How to: Debug 64-bit Applications:
 2005 - http://msdn2.microsoft.com/en-us/library/ms184681.aspx (http://msdn2.microsoft.com/en-us/library/ms184681.aspx)
 2008 - http://msdn2.microsoft.com/en-us/library/ms184681(VS.80).aspx (http://msdn2.microsoft.com/en-us/library/ms184681(VS.80).aspx)
 

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