gnuplot 4.x not using X libraries

[Joel Hammer]

I have used gnuplot 3.7 happily but I have installed
versions 4.x and I can't plot to the X terminal. I see
this message after I configure gnuplot from sources:

==============================================================

gnuplot will be compiled with the following terminals:

 X Window System terminal: no (requires X libraries)

=============================================================================

Here are is the output of 
./configure -h | grep X

X features:
  --x-includes=DIR    X include files are in DIR
  --x-libraries=DIR   X library files are in DIR
  --with-x                use the X Window System
                          (default PREFIX/share/PACKAGE/VERSION)


I am not sure what libraries I need to give (X11, X11R6)
or where the includes are. I have an old version of Linux
and X11 to be sure.

X -version gives:
==================

XFree86 Version 4.3.0.1 (Debian 4.3.0-0pre1v4.0.0.lindows0.1.0.6 20040201132350 root@)
Release Date: 15 August 2003
X Protocol Version 11, Revision 0, Release 6.6
Build Operating System: Linux 2.4.20 i686 [ELF]
Build Date: 01 February 2004
        Before reporting problems, check http://www.XFree86.Org/
        to make sure that you have the latest version.
Module Loader present
OS Kernel: Linux version 2.4.24 (root at khaffeine) (gcc version 2.95.4 20011002 (Debian prerelease)) #1 Mon May 17 04:48:14 PDT 2004 TF

===================================

Any insight appreciated.

Thanks,

Joel