<p>How can I make my compilation optimized for Windows 64 bit?</p>

A managed project is automatically built according to the architecture selected => default C# project created on AMD64 will be AMD64, X86 on X86.  The native one is always 32-bit by default.
To explicitly set a platform:
1 open the solution explorer, select solution, right click->Configuration Manager.
2 go to 'Active Solution Platform', click New.
3 in the 'New Solution Platform' dialog that comes up select the new platform say Itanium. Set 'Copy Settings From' to 'Any CPU' which was the default setting in the 'Active Solution Platform'.
4 click OK.
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