libX11 not found

[Tony Wang <TonyWang iThinkSH com>]

I have download gtk+ 2.2.1 from web site and prepare to install it.

First I upgrade all need libraries such as pango, glib2, pkg-config,

then I run ./configure, but it echo:
configure:14560: error: *** libX11 not found. Check 'config.log' for more details

There is someone say must install XFree86-devel package, but i have compile
and install the XFree86 directly, and in /usr/X11R6/lib, type "ls libX11*"
get: libX11.so  libX11.so.6  libX11.so.6.2

and type "ldconfig -v | grep libX11"
get: libX11.so.6 -> libX11.so.6.2

Why can't configure???

My system is Redhat 8.0, kernel is 2.4.14-18

Help me!