problem with configure

[tangotln]

Hi all,
I've been trying to compile some programs each time using the serie of
function: ./configure ; make and make install, but I often get, while
executing ./configure:
    checking for X.... no
I'm running RedHat 6.0 with kernel 2.2.5 and I' m using X with Xfree86
3.3.3 (which works fine.
What's wrong with my installation ?

Thanks in advance for any help,

Tanguy