ターゲットプラットフォームにx64がでない（Itaniumも）
解決方法
http://blogs.msdn.com/karinm/archive/2009/06/15/win-7-sdk-rc-can-disable-x64-config-platform-choices-in-vs2008-rtm.aspx
Windows7SDKうんぬんとかいてあるけど、
この方法でうまくいった。
Open the Control Panel.
Select "Uninstall a program" from the Programs group.
Uninstall "Microsoft Visual C++ Compilers 2008 Standard Edition - enu - x64"
Uninstall "Microsoft Visual C++ Compilers 2008 Standard Edition - enu - x86"
Right-click on the main Visual Studio entry in the program list and select "Uninstall/Change"
When the Visual Studio setup dialog appears click the Next button and then click on the "Repair/Reinstall" option.
Install Visual Studio 2008 SP1 if it is not already installed on the machine.
