How does one do "registration of SDK with Visual Studio"?

My commit f3f6c9be9864088b94f874c6ef2ce8ab1dd45f2a. was reverted (so I
can't now compile lcms2 for instance), and I also see the same problem
(windows.h not found) when compiling ICU. In the reverting commit,
Fridrich says "registration of SDK with Visual Studio [2008] seems to
be the answer". How do I do that?

(I recently uninstalled the Windows SDK 7.0 and installed SDK 7.1, and
apparently it registered itself only with VS2010. The reason why I
wanted to install a fresh Windows SDK was that for some months, my
"Windows SDK Documentation" application had not been able to display
the (local) documentation normally; it displayed the HTML source and
then offered in a top bar something like "click here if you want to
see the formatted context". That was a bit annoying. So I thought
maybe installing the freshest SDK will work better. Ha ha. Now I have
no SDK documentation working locally at all... Oh well, the docs on
the net work fine.)

--tml