When starting with a new project, sometimes it is helpful to keep x64 in mind from the very beginning.
- From the "Build" menu, select "Configuration Manager".
- Under the "Active Solution Platform", select "<New...>".
- Select "x64" from the new platform type.
(If it is not available, you need to modify your VS2005/VS2008 installation by inserting the DVD and selecting x64 compiler under C++)
- Copy settings from "Win32".
- Ensure that the "Create new project platforms" checkbox is ticked.
- OK to save.
Now in your main window, select between x86 and x64 by changing the selection in the dropdown.