alt Hacker NewsAs far as I'm aware so long as you limit yourself to APIs that were available in XP you don't actually need an older SDK to develop for it with modern MSVC. The early windows platform layer stuff in the handmade hero series demonstrates doing so without anything like Cygwin or MinGW.
Most new APIs introduced since Vista are COM based, and after Windows 8, WinRT based (basically COM with IIinspectable, application identity, and .NET metadata instead of type libraries).
Plain old Win32 C API is basically frozen on Windows XP view of the world, although there are a couple of new .....ExNum() suffixes for stuff like HDPI or various IO improvements, the userspace drivers initially COM (UMDF), but reverted back to plain C struct with function pointers on version 2.0.