From MSDN:
Target Platform Version
[…]
To target Windows 7 or Windows Vista, use the value 8.1, since Windows SDK 8.1 is backward compatible to those platforms. In addition, you should define the appropriate value for _WIN32_WINNT in targetver.h. For Windows 7, that’s 0x0601. See Modifying WINVER and _WIN32_WINNT.