Cant install root v16 on os x leopard

Hi,

I cannot configure root to install. I did after upgrading to leopard:

make clean
./configure

and see during configure:

Macintosh-5:root_v516 markhodgkinson$ ./configure
machdep: class is not implemented
Configuring for macosx
Checking for libX11 … /usr/X11R6/lib
Checking for X11/Xlib.h … no
configure: X11 headers (package x11-devel) MUST be installed

I do have x11 though. Does someone know the solution?

Cheers,

Mark