If Win7 SDK (RC) is installed SidebySide with Visual Studio 2008 RTM before Visual Studio 2008 SP1 is installed, x64 and Itanium platform will not be available from the New Platform drop-down list. Build targeting x64 and Itanium will also fail. To work around the issue, please refer to this post. Note that the issue has been fixed in Win7 SDK RTM.
Visual C++ Team