non-US keyboards

yeah i'm very very newbie but... i won't a keyboard for my language!

where are Xlib.h Xutil.h Xatom.h ecc???

i'm trying to compile a small program (that uses Xforms) make requests: X11/Xlib.h X11/Xutil.h X11/Xatom.h X11/keysum.h X11/Xresource.h X11/cursorfont.h where are they placed? /usr/include/X11 is absent!