The GDK docs werent updated for either the november08 update or the 7.3 update.
If I might suggest, have a look through all of the header files, you can generally discover a number of undocumented features that way, most of the time they are pretty self explanatory as to how they work.
But you dont need the update to be able to find out the size of your window on your desktop, which is what those commands above do I assume(ive not used em). Just create a RECT struct, and call the appropriate windowsAPI function, passing it the handle of the GDK window(g_pGlob->hWnd) ... although u need to include "globstruct.h" and "windows.h".
If it ain't broke.... DONT FIX IT !!!