[ns] "can't find X library" error in ns-2.26 installation

[Bringo Shawn]

Hello there,
For
some reasons I have to install ns-2.26, although I know that the latest
version is ns-2.34. At './install', I got these errors:
...
tclcl-1.0b13 has been installed successfully.
============================================================
* Build ns-2.26
============================================================
loading cache ./config.cache
...
checking for tcl2c++... ../tclcl-1.0b13
checking for X11 header files
checking for X11 library archive
checking for XOpenDisplay in -lX11... (cached) no
can't find X library
Ns configuration failed! Exiting ...
Please check http://www.isi.edu/nsnam/ns/ns-problems.html
for common problems and bug fixes. 

After applying the patch mentioned at http://www.isi.edu/nsnam/ns/ns-problems.html#tclcl-1.0b13, I am facing these errors:
...
tclcl-1.0b13 has been installed successfully.
============================================================
* Build ns-2.26
============================================================
loading cache ./config.cache
No .configure file found in current directory
Continuing with default options...
...
checking for X11 header files
checking for X11 library archive
checking for XOpenDisplay in -lX11... (cached) no
can't find X library
Ns configuration failed! Exiting ... 
Please check http://www.isi.edu/nsnam/ns/ns-problems.html
for common problems and bug fixes. 

I am using fedora 9, and GCC version is gcc (GCC) 4.3.0 20080428 (Red Hat 4.3.0-8). Please help me.
Best Regards.