Problem in installing NS(all in one)

[Atul Suresh Joshi]

Hi,
We are running into some problem.
We have downloaded version :  ns-allinone-2.1b2.tar.gz
When we give "./install following error occurs.

...
...
checking for X11 header files... couldn't find any!
...
...
-----------------------------------------------------------------------
cpp: "tk.h", line 74: error 4036: Can't open include file 'X11/Xlib.h'.
*** Error exit code 1

Stop.
tk8.0 make failed! Exiting ...
-----------------------------------------------------------------------
Could you please send me a mail about a possible remedy
for this?

Thank you
atul